Having a number of English frames to build up, I've been trying to accumulate some old style GB stems. On a frame with a 55 cm top tube, I typicall use an 80 mm extension, but I have not found a GB in that size, although there seem to be plenty of 75 mm. This makes me suspect that GB stem extensions were sized in inches, not mm. Is that the case? 3" would be 76.2 mm, which one could easily measure as 75 mm. 4" would be 102.6 mm. If GB stems were sized in inches, were they available in half inch increments, or only whole inches? 3 1/2" inches would be 88.9 mm, still a bit long for me on most frames, and I'm not even sure I've seen a GB in that extension.
Regards,
Jerry Moos
Big Spring, TX