The M54 to M42 male adapter is a popular male to male adapter.  Often used between an electronic filter wheel and the ASG photon cage M54, this allows a solid connection on both ends.

Product Description:

• Adapter for use with cameras with large sensors and accessories with M54x0.75 threads offered by companies like ZWO, Atik, Trutek, etc.
• Features an M54x0.75 male thread on one side and an M42x0.75 T/T2 male thread on the other side
• Not for use with accessories that have an M54x1 thread
• Precision machined, black anodized aluminum

Specifications:

• Weight = 0.5oz
• Total length = 9mm (0.35")
• T/T2 male thread specification = M42x0.75
• Length of T/T2 male thread (including unthreaded undercut) = 4.1mm (0.16")
• M54 male thread specification = M54x0.75
• Length of M54 male thread (including unthreaded undercut) = 3mm (0.12")
• Optical length = 1.9mm (0.07")
• Clear aperture = 38.8mm (1.53")
• Maximum outside diameter = 67.8mm (2.67")