i have 2 fastechs,and they both had the same problem.their collets were overtightened at the factory,and then when you loosen them to lube the shaft,they wont tighten again.i just ordered a couple of proboat replacements and havnt overtightened them,havnt had a problem since.i think the flex diameter is .150.if your heart is set on OSE replacements,give them a shout or look on their forums,they're a great bunch over there,they have helped me out quite a bit.