For convenience of use, the Duo-Art Temponamic knob is permanently
attached to a piece of heavy, hollow brass tubing designed to permit
its extension to about two inches away from the keyslip.  At the
tail end of this tube is a tiny screw which may be viewed from the
left, underneath, with the knob all the way in and turned clockwise
as far as it will go.

This screw holds in place an "aliquot" (to use the Mason & Hamlin
term for a similar-looking part), which confines the in-and-out
movement of the knob to a half-round section of the shaft going
into the tube.  The screw is in a position of difficult access and
you will need a jeweler's screwdriver of appropriate size.

But please be forewarned: It's an extremely easy part to lose;
removal of the keyslip and roller support will make the job easier
and safer.  Once the screw is out the knob can be pulled off and
the aliquot (also easy to lose) may be removed.

Jeffrey Wood