BSA Clutch Puller / Extractor M20 WD Model. For 1 Spring Clutch AD: 1" -25.4mm. 24TPI UNEF. early C10, C11 pulls P.Nr.65-3913. The BSA clutch centres can vary, very tight and when you use the Puller, you should slightly tighten it, tap it with a hammer and if this does not work, apply WD40, repeat the process and leave it overnight.