On many threading dies both sides are tapered and I find it difficult to ascertain the leading edge. It seems on most the labeling, i.e. 1/4-20, is facing outwards, away from the direction of feed, but occasionally i would swear this ain't so. What you say? It's driving me nuts, pun intended. The second I would like to think I originated over fifty years ago while working for Cummins engine Co. goes like this, piston comes to dead stop at TDC and BDC (or as the Brits say inner and outer DC from horizontal engine days). There are three logical geometric places where one might assume max piston velocity occurs. All are wrong except on an engine which has never been built and on that engine all are correct. Name the three geometric points, the engine which never has been built and the location of maximum piston velocity on an actual engine. thanks for your time, Ian.