Bleeder thread sizes
 

I ordered a set of speed bleeders back in Nov 09; planned to install when I bled my brakes in the Spring. When I inserted the speed bleeder spec'd for the M calipers on the right-rear caliper and started to tighten, it felt loose in the hole, so I removed it and mic'd it; the thread is smaller than the bleeder I removed. The Speed bleeder measures 0.26" across at the thread while the bleeder I removed measures 0.31" across at the thread. So I pulled the bleeder on the left rear...same thing. Pulled the left front bleeder...same thread as both rears...the bleeders on the car are all interchangeable, despite the calipers being different fro to rear. I tried the Speedbleeder PEL-SB8125LL designed for the front "A" calipers (Ate 17G) on the rear "M" calipers (Ate 5G) and they fit. Has anyone seen this before? Did the factory make a running change? Could the PO had the rear caliper bleeders break off and drilled out and threaded for these larger ones? Appreciate any thoughts/ feedback.

Part number for the rear calipers is wrong. The rears take the same one as the fronts. Its been discussed before.

The threads on the bleed nipples are 7mm x 1.0 pitch except for those calipers with cross-over lines (L calipers on the rear of 1965 to 1968, aluminum S calipers, and so on) which take the 10mm x 1.0 bleed nipples. This probably does not cover all possible calipers though. I once ordered a package of 100 nipples from a UK supplier, but they turned out to be 6mm for the VW.