The SM1A18 thread-to-thread adapter contains an internal SM1 (1.035"-40) thread and an external M27 x 0.75 thread. Made of anodized aluminum, it is machined with the two threads connected by a flange and can be placed at the end of a threaded tube. It is typically used to create an objective from an SM1 lens tube. The unpackaged weight of this adapter is 3.63 g.