Thread spec for your 81-138?
A quick learner from Lake Gaston, NC says:
May 20, 2012
I purchased replacement rollers from a competitor (Prime-Line). The threaded insert that holds the assembly in place was, in the original, a #10 bevel head screw. The replacement roller had threaded this for a 1/4-20 screw. The shortest available screw is 1/2" and the diameter of the larger screw prevents the adjuster from moving to allow the rollers to lower. I compensated for this by using nylon spacers to limit the depth, but the P-L unit, as designed, is unworkable. My question to you is what is the thread spec on your 81-138 roller?
Dave from SWISCO responded:
May 22, 2012
Thanks for posting! Do you mean the installation hole above the adjustment screw? If so, it has a 1/4-20 thread count. The hole on the top, however, is not threaded, though it looks like a 3/16" hole.