Graywolf wrote:
OK, I just pulled one, it is a "recessed binderhead phillips machine screw"
In the UK, sometimes called "panhead" or, if somewhat thicker, "cheesehead". Also called "setscrews". Good series of diagrams here:
http://www.smithfast.com/iscrew.htm
Screws on Pentax lenses will certainly (crosses fingers and looks skyward) be metric. Size, small. 8-) BA (British Association) is what they would have been when people could use more then their fingers and other digital machines to do arithmetic. It is a fine pitch thread usually used in model making and electrical work. As with most imperial measurements and their applications it was designed by engineers based on practical experience, not the mutterings of a committee based on the wavelength of a particular colour of light.
mike
