A guide for a bone cut comprises a guide base having an inner wall defining an opening. The inner wall has a plurality of detents distributed around the opening. The guide base has a proximal surface adapted to contact a skin of a person. An inner collar has one or more spring loaded devices extending outward from the inner collar in opposite directions. The inner collar is mountable with the spring loaded devices fitting within one or more of the plurality of detents. The inner collar has an inner wall defining a bore for receiving a cutting tool. The inner collar is configured to pivot the cutting tool about an axis, for cutting a bone. The axis lies along or parallel to a line along which the spring loaded devices lie.