how are the stem sizes actually looked at? ive got a stem that reads 25.4 mm (1 inch) and im looking at a threadless adapter that says it fits 1 inch steering tubes (it also says that 1 inch = 22.2mm)
what i guess im really asking is. if the opening of the steering tube is and inch, and the stem itself is an inch. and both equal 25.4mm, then why do all the sites i look at say the one inch is 22.2mm. does it mean that my steering tube is considered a 1 1/8 inch? or and i just getting screwed up with all the diameters(inside/outside) if someone could shed a little light on this it would be greatly appreciated!!!
You've got your ends mixed I think. The mix of units is the clue. A MTB bar clamp may be exactly 1 inch, but it is specified as 25.4mm to contrast with the 26mm road clamp size.
So I'm guessing you're looking at adapting a threadless-type stem to a 1" threaded fork? 22.2mm is the INSIDE diameter of a 1" threaded steer tube. So a quill-type stem, or the bottom of a threadless adaptor is 22.2mm to slide down into the tube. Then the part of the adaptor will be 1-1/8" to fit a 1-1/8" threadless stem. Threadless steer tubes don't have a standard inside diameter. It just doesn't matter. Not sure what the inside diameter of an 1-1/8" threaded steerer is. I'd measure but can't find my calipers in the garbage pit I call a garage!
First figure out what you have. Measure the O.D. and determine if its threadless or threaded. If it's threadless, it'll most likely be 1-1/8" and just get a standard 1-18" stem. If it's threaded, get a standard 1-1/8" stem and one of these to match your measured O.D.:
Don't get blown out into the weeds with the measurements. Your stuff IS standard - I guarantee it. So just get stuff that says it matches the standard. An MTB stem in whatever length and rise you want to fit you, then the adaptor you need - either an adaptor for 1-1/8" or 1".
The only complication with a threadless stem is if it's Oversized or not. This just refers to the bar clamp and just means if you get an O/S stem, you'll need an O/S bar.