Just a couple of cautionary notes:
1. They are made to fit on the tek-na-tools chucks, Supernova and G-3. There is a ridge line that runs around the jaw plate that makes the fit on other chucks problematic.
2. Note that there is only one hole in the jaws for the screw. The Nova chucks all are made to accomodate two screws per jaw. This introduces a potential problem with securely holding the jaws to the chuck.
3. the length of the jaws (necessary to accomodate the pen blank), combined with the single screw hole can intoduce some issues when drilling. Mainly, not a secure enough hold on the blank, which can make your holes less precise than you generally want.
All in, these issues can be overcome, but wanted you to know some things to watch for.