butlersrangers wrote on Mar 11^th, 2014 at 3:13pm:

ButterBolt:  It is all done with friction.  When the lever is pushed to the right, (toward the 'center-line' of the barrel/sight base), it 'rides down' on an inverted screw's thread.  This clamps the two parts of the sight base together.  If parts are clean, it does not take very much effort to move the lever to lock or release.  (Attached picture shows 1901 sight from the bottom with lever in 'locked' position).

You do need to be sure the screw is properly seated, and that the sight base fits snug to the barrel, since the screw head is hollowed out for the curvature of the barrel. If improperly assembled, the lever will never lock. Start with the lever swung all the way out to the left, and jockey things until everything is snug and it starts to bind up when straight ahead.