My C head takes B3 slotted collets. I haven't had it very long and just today, for the first time actually looked up inside the spindle. It was really hard to tell, but it looks like the protrusion that goes into the collet slot used to be a long piece that has broken off, leaving only a tiny fragment of steel at the lowest part. All that goes into the slot is a little piece of steel maybe a couple millimeters long. I always thought that there was a long piece of steel that the collet slid into. So is it supposed to be a long piece in there, or just a little tab? Just wondering if one of these days that last little piece is going to break off. If it did, would that even be a problem? Some collets don't have the keyway at all, so I assume it would be alright. My head is from the 1930's, so is that keyway just an old thing that has come to be obsolete and the collet doesn't really need to stay put?