[donbga]

Pretty much, yes. Most enlarging lenses made since the 1970s for 35mm and medium format use M39 (Leica thread mount). For bigger lenses starting around 135mm, you may need a larger lensboard hole, and some short lenses designed for formats like 110 may have had smaller mount sizes.

Generally that's true. However some of the exotic enlarging lenses made by Nikon for example had a much larger mounting diameter. Of course those types of lenses cost thousands and were never intended for the amateur darkroom enthusiast.