Products HomeScrew Thread Adapters
- Imperial, Metric, and Imperial-Metric Adapters
- M3, M4, M6, 4-40, 6-32, 8-32, and 1/4"-20 Thread Adapters
- Useful for Mounts, Posts, and Post Holders
- Two Types of Counterbore Adapters
AI25E8E
Internal 8-32
Internal 1/4"-20
AS4M8E
Internal M4 x 0.7
External 8-32
CBA25E
1/4"-20 Thread
0.40" Outer Diameter
AE8E25E
Internal 8-32
External 1/4"-20
AP6M8E
External M6 x 1.0
External 8-32
MSA8
Internal 4-40
External 8-32
MSA25
Internal 4-40
External 1/4"-20
HW-KIT6
Thread Adapter Kit
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| External to External |
| Internal Threading with External Threaded Stud |
| Internal to External |
| Internal to Internal |
| Threaded Counterbore |
| Counterbore Adapter Rings |
| Screw Thread Adapter Kit |
Figure 1.1 Rail Carrier Cross Section with SD1 Counterbore Adapter Ring
Threading Adapters
- Machined from 303 Stainless Steel
- Adapt One Common Thread Standard to Another
- Ideal for Mounting Posts
Thorlabs' selection of thread adapters offers numerous options for switching between M3, M4, M6, 4-40, 6-32, 8-32, and 1/4"-20 thread sizes. Choose from internal-to-external, external-to-external, or internal-to-internal thread adapters. We also offer internal-to-external threaded stud adapters. Our external-to-external and internal-to-external thread adapters can be adjusted with a screwdriver on either end. The internal-to-internal thread adapters and internal-to-external threaded stud adapters feature a through hole to provide additional torque when tightening or loosening.
The Mini-Series thread adapters can be used to make the Mini-Series posts compatible with our extensive range of optical mounts.
Counterbore Adapters
Threaded counterbore adapters are used to convert a counterbore to a threaded hole. A part such as the KM100 kinematic mirror mount features counterbores to provide imperial and metric compatibility. A cap screw is typically used to fasten these mounts to a post, but in some instances it is necessary to attach the mount to a post with a fixed threaded stud. The counterbore adapter allows parts, such as the KM100, to be post mounted when a cap screw cannot be used.
The SD1 is an adapter ring that provides a means to attach 8-32 (M4) tapped components to 1/4"-20 (M6) counterbored parts. One possible use for the SD1 is in a dovetail optical rail setup where the RC1 rail carriers feature a 1/4" (M6) counterbore. Optic mounts are commonly attached to RC1 rail carriers and usually require the SD1 adapter as most optic mounts are 8-32 (M6) tapped.
Thread Adapter Kits
Thread Adapter Kits are available in both imperial and metric varieties. Both kits come packaged in an organizing box with convenient scaled drawing labels and contain our most popular thread adapters. See below for a list of the specific adapters contained in each kit.
| Posted Comments: | |
user
(posted 2025-05-10 19:53:26.65) Hi, I have a use for an internal 1/4-20 to external 2-56 or M2 adapter. Like AE4E25E, but with 2-56 or M2x0.4 internal threading. jdelia
(posted 2025-05-12 02:10:36.0) Thank you for contacting Thorlabs. At this time, we unfortunately do not offer this type of screw thread adapter. I have reached out to you directly via email to discuss your application and potential alternative solutions. user
(posted 2025-03-06 14:30:33.647) Is it possible to produce 4-40 to M3 external-external thread adapter? felix reid
(posted 2022-06-18 19:27:08.603) Hi,
I need an adaptor M6 x 1mm to M3 x 0.5mm external to external thd. A step down post for want of a better expression. Ideally, in brass but steel will do if zinc or similar plated jdelia
(posted 2022-06-20 12:47:00.0) We unfortunately do not offer any M6 external to M3 external thread adapters. The closest solution that could be achieved with our products would be using an external-internal M6-M4 adapter like AE4M6M and an external-external M4-M3 adapter like AP4M3M. All of our screw thread adapters are made from 303 stainless steel. user
(posted 2022-03-08 04:42:51.747) Hello,
Would be better if the adapters could be sold in pack of 10, 20 or more. For quantity order, unpacking every individual adapter takes time. The kit you propose offers only 5 times the items and some are more used than other.
Thank you
PS : similar comment than "hanneke (posted 2010-02-17 12:20:53.0)" jdelia
(posted 2022-03-11 09:21:48.0) Thank you for the feedback! I have passed along your request to our internal suggestion forum. I have also contacted you directly regarding your application. Mark Handschy
(posted 2020-02-17 10:55:23.187) product description "External 8-32 Threads and Internal 4-40 Threads" seem to contradict part drawing (autocad pdf) llamb
(posted 2020-02-18 04:24:43.0) Thank you for your feedback on our MSA8 thread adapter. After discussing this directly by email, the PDF drawing is indeed correct and matches the description. There is an externally (male) threaded #8-32 stud and an internally (female) threaded #4-40 hole on the other end, which happens to sit within a Ø6 mm counterbore. Ludovic Angot
(posted 2020-01-03 02:10:39.32) Hello, could you offer an external 4-40 to external M4 adapter, of the same style as your AP8E4E / AP4M3? This would allow, among other usages, to mount any M4 component (be them threaded or counterbored) on 6mm cage rodes. llamb
(posted 2020-01-07 10:19:53.0) Hello, thank you for your feedback. I have added this idea to our internal product forum for further consideration, and have reached out to you directly to discuss your application as well. Ludovic Angot
(posted 2019-09-19 08:53:39.333) Hello, I, certainly like other customers, purchase several thread adapter types at once. Would it be possible you think about a way to offer a pack of e.g. 4 (as for your cage assembly rods) of the same adapter for some (or better, all) of your thread adapters? That would save you on packing, packing time, reduce waste and be more convenient and economical for your customers. YLohia
(posted 2019-09-19 09:38:43.0) Hello, thank you for your feedback. I have posted your request for multipacks of our 4-40 / M3 thread adapters on our internal engineering forum for further consideration. tjschongar
(posted 2018-07-29 12:36:50.47) MSA8 MINI What thread pitch is the 8-32side? unc of unf i need to get the right tap size YLohia
(posted 2018-07-30 09:43:00.0) The thread count is 32 threads in an inch, which translates to 0.79375 mm pitch. The 8-32 thread is UNC. keweima
(posted 2015-03-10 16:47:33.74) Do you carry anything like this but for a M2.5 thread instead of M3? cdaly
(posted 2015-03-25 02:12:57.0) Response from Chris at Thorlabs: We did at one time offer M2.5 adapters to 1/4-20 threads as a standard part, AE25M25E, but this has since been obsoleted. I will look into the possibility of offering it as a custom and contact you directly. iain
(posted 2014-09-04 12:55:30.963) Do you make an adapter with external M4 and external 1/4"-20 threads? This would be useful for screwing the M4 end of a 12.7 mm Ø post into an imperial optical table. cdaly
(posted 2014-09-04 10:02:05.0) Response from Chris at Thorlabs: There's no external to external adapter, but we do have an internal to external one that should work for you. AE4M25E would thread over the M4 stud which comes with the metric 1/2" series posts and leave you with external 1/4-20 threads, allowing you to mount the M4 side flush with an imperial the table. Adam
(posted 2010-05-17 15:18:58.0) A response from Adam at Thorlabs to makarov: Thank you very much for the customer inspired new product idea. I agree that this would be a great addition to the catalog and fill and important void in our thread adapters. I am currently working on a quotation for these custom thread adapters and will confirm the dimensions of the custom product via email. makarov
(posted 2010-05-16 01:43:11.0) I would like to buy AP4M4E adapter, external M4 to external #4-40 thread, length 9.5 mm (unfortunately not in your list). I need 20-30 pieces initially. The reason is that we are a metric lab but we have started to use MiniSeries and decided to reuse your standard 6 mm diameter cage rods as posts in MiniSeries, instead of buying separate 6 mm diameter MiniSeries posts (which would add clutter and confusion in the lab as new students try to interchange them with the cage rods). Its quite strange that this thread adapter is not a stock item, given your wide assortment. Right now we have to use two thread adapters on top of one another to mount an M4-threaded component to a cage rod; we have also tried to double-tap M4 holes with #8-32 tap to make it fit a single thread adapter, but I doubt the latter is a good idea lab-wide. apalmentieri
(posted 2010-02-17 15:15:44.0) A response from Adam at Thorlabs to Hanneke: We are currently in the process of evaluating the packaging of all of our products. We are updating the packaging to make them more environmentally friendly. Thank you for the suggestions, I agree that this is a good idea and we will get started on changing this packaging. hanneke
(posted 2010-02-17 12:20:53.0) I just ordered a bunch of thread adapters and have spent the morning unwrapping each individual screw. It seems that you could save yourself money and your customers time by putting the screws in ziplock bags based on part number in the quantity ordered (e.g. all the AP6M8E screws in the same bag). I do appreciate the perforations on the baggies, though. Laurie
(posted 2008-10-15 12:01:49.0) Response from Laurie at Thorlabs to dsmith: It is possible for our machine shop to do some custom machining, but we would need you to provide us with a drawing of your exact requirements prior to quoting you the cost. Thanks for your interest in our products, and please let us know if we can be of further assistance. dsmith
(posted 2008-07-18 07:14:57.0) I am looking for an adapter for use on an angle grinder with a 5/8" female thread to attach an M14 internally threaded cone. I would be looking for a quantity of approx. 50 pcs.
Any assistance would be appreciated.
Best Regards,
Darragh Smith
Technical Sales
Abcon Industrial Products
Cavmac Hose Building
Cavan Road
Cootehill
Co Cavan
Ireland |
Zoom| Item # | Thread A (External) |
Thread B (External) |
Length C |
|---|---|---|---|
| Imperial Thread Adapters | |||
| AP8E4Ea | 8-32 | 4-40 | 0.38" (9.7 mm) |
| AP8E25Ea | 8-32 | 1/4"-20 | 0.57" (14.5 mm) |
| Imperial/Metric Thread Adapters | |||
| AP8E4Ma,b | 8-32 | M4 x 0.7 | 0.48" (12.2 mm) |
| AP25E6Ma,b | 1/4"-20 | M6 x 1.0 | 0.57" (14.5 mm) |
| AP6M8Ea,b | M6 x 1.0 | 8-32 | 0.57" (14.5 mm) |
| Metric Thread Adapters | |||
| AP4M3Mb | M4 x 0.7 | M3 x 0.5 | 0.38" (9.7 mm) |
| AP6M4Mb | M6 x 1.0 | M4 x 0.7 | 0.57" (14.5 mm) |
Zoom
Click to Enlarge
Figure G2.1 The MSA8 Thread Adapter converts an 4-40-threaded stud into an 8-32-threaded stud.
| Item # | Thread A (Internal) |
Thread B (External) |
Length C | Outer Diametera |
|---|---|---|---|---|
| Imperial Thread Adapters | ||||
| MSA8 | 4-40 | 8-32 | 0.50" (12.7 mm) | 0.40" (10.2 mm) |
| MSA25 | 4-40 | 1/4"-20 | 0.55" (14.0 mm) | 0.50" (12.7 mm) |
| AS6E8E | 6-32 | 8-32 | 0.56" (14.2 mm) | 0.24" (6.0 mm) |
| AS8E25Eb | 8-32 | 1/4"-20 | 0.68" (17.3 mm) | 0.40" (10.2 mm) |
| AS25E8Eb | 1/4"-20 | 8-32 | 0.61" (15.4 mm) | 0.40" (10.2 mm) |
| Imperial/Metric Thread Adapters | ||||
| AS8E4M | 8-32 | M4 x 0.7 | 0.56" (14.2 mm) | 0.25" (6.4 mm) |
| AS8E6M | 8-32 | M6 x 1.0 | 0.68" (17.3 mm) | 0.40" (10.2 mm) |
| AS25E4M | 1/4"-20 | M4 x 0.7 | 0.61" (15.4 mm) | 0.40" (10.2 mm) |
| AS25E6M | 1/4"-20 | M6 x 1.0 | 0.63" (16.0 mm) | 0.38" (9.5 mm) |
| AS4M8E | M4 x 0.7 | 8-32 | 0.56" (14.2 mm) | 0.25" (6.4 mm) |
| AS4M25E | M4 x 0.7 | 1/4"-20 | 0.68" (17.3 mm) | 0.40" (10.2 mm) |
| AS6M8E | M6 x 1.0 | 8-32 | 0.61" (15.4 mm) | 0.40" (10.2 mm) |
| AS6M25E | M6 x 1.0 | 1/4"-20 | 0.63" (16.0 mm) | 0.38" (9.5 mm) |
| Metric Thread Adapters | ||||
| MSA4/M | M3 x 0.5 | M4 x 0.7 | 0.50" (12.7 mm) | 0.40" (10.2 mm) |
| MSA6/M | M3 x 0.5 | M6 x 1.0 | 0.55" (14.0 mm) | 0.50" (12.7 mm) |
| AS4M6Mc | M4 x 0.7 | M6 x 1.0 | 0.68" (17.3 mm) | 0.40" (10.2 mm) |
| AS6M4Mc | M6 x 1.0 | M4 x 0.7 | 0.61" (15.4 mm) | 0.40" (10.2 mm) |
Click to Enlarge
Figure G2.2 Mini-Series Thread Adapters
Zoom| Item # | Thread A (Internal) |
Thread B (External) |
Length C |
|---|---|---|---|
| Imperial Thread Adapters | |||
| AE4E25Ea | 4-40 | 1/4"-20 | 0.38" (9.5 mm) |
| AE6E25E | 6-32 | 1/4"-20 | 0.38" (9.5 mm) |
| AE8E25ES | 8-32 | 1/4"-20 | 0.20" (5.1 mm)b |
| AE8E25Ea | 8-32 | 1/4"-20 | 0.38" (9.5 mm) |
| Imperial/Metric Thread Adapters | |||
| AE4E6M | 4-40 | M6 x 1.0 | 0.39" (10.0 mm) |
| AE6E6M | 6-32 | M6 x 1.0 | 0.39" (10.0 mm) |
| AE8E6M | 8-32 | M6 x 1.0 | 0.39" (10.0 mm) |
| AE3M25E | M3 x 0.5 | 1/4"-20 | 0.38" (9.5 mm) |
| AE4M25E | M4 x 0.7 | 1/4"-20 | 0.38" (9.5 mm) |
| Metric Thread Adapters | |||
| AE3M6Mc | M3 x 0.5 | M6 x 1.0 | 0.39" (10.0 mm) |
| AE4M6MS | M4 x 0.7 | M6 x 1.0 | 0.20" (5.1 mm)b |
| AE4M6Mc | M4 x 0.7 | M6 x 1.0 | 0.39" (10.0 mm) |
Zoom| Item # | Thread A (Internal) |
Thread B (Internal) |
Length C | Outer Diameter |
|---|---|---|---|---|
| AI25E8E | 8-32 | 1/4"-20 | 0.50" (12.7 mm) | 0.40" (10.2 mm) |
| AI6M4M | M4 x 0.7 | M6 x 1.0 | 0.50" (12.7 mm) | 0.40" (10.2 mm) |
Zoom
- Converts a Counterbored Clearance Hole into a Tapped Hole
- Slotted Edge for Tightening
- Designed for Slip Fit with Thorlabs' Counterbores
Threaded counterbore adapters are used to convert a counterbore into a threaded hole. A part such as the KM100 Kinematic Mirror Mount features a counterbore that provides imperial and metric compatibility; a cap screw is typically used to fasten the mount to a post. In some instances, it may be necessary to attach the mount to a post with a fixed threaded stud. The counterbore adapter facilitates this mounting option. These adapters feature a slotted edge that enables tightening or removal.
| Item # | Thread A (Internal) |
Outer Diameter B | Use in C-Bore |
|---|---|---|---|
| CBA8E | 8-32 | 0.28" (7.0 mm) | #8 |
| CBA25E | 1/4"-20 | 0.40" (10.2 mm) | 1/4" |
| CBA4M | M4 x 0.7 | 0.28" (7.0 mm) | M4 |
| CBA6M | M6 x 1.0 | 0.40" (10.2 mm) | M6 |
Zoom
Figure G6.1 Rail Carrier Cross Section with SD1 Counterbore Adapter Ring
- Allows a #8 (M4) cap screw to be used within a 1/4" (M6) counterbore
- Solid stainless steel design
- Sold in packages of 10
The SD1 adapter ring allows a #8 (M4) cap screw to be used within the 1/4" (M6) counterbore of many parts including rail carriers, BA2 mounting bases, etc. Most of our optomechanical components, such as our compact mirror mounts, feature tapped 8-32 (M4) holes, which this adapter is designed for. For example, the VC1 small V-clamp can mount directly to a BA1 base when an SD1 adapter is used with a 8-32 cap screw.
Zoom
| Table G7.1 HW-KIT6 Imperial Thread Adapter Kit | |||
|---|---|---|---|
| Item | Qty. | Item | Qty. |
| SS* External 8-32 and External 1/4"-20 (AP8E25E) | 5 | SS* External 8-32 and External M4 x 0.7 (AP8E4M) | 5 |
| SS* Internal 8-32 and External 1/4"-20 (AS8E25E) | 5 | SS* External 8-32 and External 4-40 (AP8E4E) | 5 |
| SS* External M6 x 1.0 and External 1/4"-20 (AP25E6M) | 5 | SS* External 8-32 and Internal 1/4"-20 (AS25E8E) | 5 |
| SS* External 8-32 and External M6 x 1.0 (AP6M8E) | 5 | SS* Internal 4-40 and External 1/4"-20 (AE4E25E) | 5 |
| SS* Internal 8-32 and External 1/4"-20 (AE8E25E) | 10 | - | - |
| Table G7.2 HW-KIT6/M Metric Thread Adapter Kit | |||
|---|---|---|---|
| Item | Qty. | Item | Qty. |
| SS* External M4 x 0.7 and External M6 x 1.0 (AP6M4M) | 5 | SS* External 8-32 and External M4 x 0.7 (AP8E4M) | 5 |
| SS* Internal M4 x 0.7 and External M6 x 1.0 (AS4M6M) | 5 | SS* External M4 x 0.7 and External M3 x 0.5 (AP4M3M) | 5 |
| SS* External M6 x 1.0 and External 1/4"-20 (AP25E6M) | 5 | SS* External M4 x 0.7 and Internal M6 x 1.0 (AS6M4M) | 5 |
| SS* External 8-32 and External M6 x 1.0 (AP6M8E) | 5 | SS* Internal M3 x 0.5 and External M6 x 1.0 (AE3M6M) | 5 |
| SS* Internal M4 x 0.7 and External M6 x 1.0 (AE4M6M) | 10 | - | - |
*Stainless Steel
Additional Screws, Kits, and Adapters
Thread Adapter Screws