OK, I said I was getting some parts machined, and they are finally in. I now have a nice adaptor ring for attaching M42 lenses to 55mm filter threads. This is the holy grail of sorts for 35mm adaptor projects. First, because good M42 lenses are plentiful and can be had very inexpensively. Second, because the M42 camera bodies were so popular, there are adaptors for other lens types to attach to the bodies. What this means is that you can use this adaptor with an M42 lens, or add another adaptor and attach pretty much any type of lens available. B&H Photo Video has a wide variety of "XXX Lens to M42 body" adaptors.

http://www.727records.com/727ad001.jpg

OK, so click the link for a picture of the adaptor ring. It is made of solid aluminum, about 9mm thick. This is a sturdy adpator. Female 42mm x 1.0mm (M42) pitch threads in the center, and male 55mm x .75mm (camera filter) pitch threads on one side. Weight is 1 ounce. I have eight (8) of these available, if you think you would find it useful. I'm try to recoup the cost of the machining. I am asking $25 in the US (includes USPS shipping), a little more for shipping outside the US. If you would like one, please email me, joshprovost at yahoo dot com. If I have any left, I will send you a PayPal money request.

Forgive my ignorance - are the M42 the Screw-in type lens for 35mm pro cameras?

Not pro, but those lenses are the ones I use on my adapter. In my country and maybe other European countries it is called P-tread, used by Pentax, pentacor, conica, practica and more.