At least that is the description I see when looking at various mirrors. the ones with the mirror held tight on the stem with a set screw. Are they "set and forget" or do they loosen and need to be tightened periodically? Thinking of changing to rectangular mirrors eventually and most seem to come in the 2 piece configuration. I have the stock tear drop single piece mirrors now and don't want to deal with mirrors loosening unexpectedly on a trip if the 2 piece ones might do that. I have heard that blue locktite is a help.

 

What do you mean by 'two piece'? I have a 1990 bike with rectangular mirrors and a new one with the tear drop style and they are identical in construction, as best I can tell. (I just got back from the garage having checked!). Neither needs any special attention to stay put, but the rectangular ones have two screws to nip them in place, if necessary.