In engineering it always amazes me how many people replace hardened steel dowel pins the wrong way round, end up damaging the reamed hole in which it is inserted, and then wonder why the doweled parts are not in alignment. Traditionally, a dowel pin will have an end which is tapered and an end which is not. The tapered end must always be inserted to the hole first or the hole will be damaged and the parts may be assembled out of alignment. In more recent years dowel pins have become available with tapers on both ends of the pin; with this type it doesn't matter which way round it is inserted into the hole. It is surprising that this is not better known.