If you have a Park Tool CRS-15 oversized crown race setting system for steerer tubes up to and including 1.5", Park now offers this CRS-15EXT which gives you an additional cylinder length for steerer tubes up to 425mm long. The plated steel Extension segment is a perfect match for your existing CRS-15, and comes with a machined aluminum spacer that acts as a loose coupling for the extension.

It couldn't be easier to use this extension, you just place the race you want to set down the steerer tube at the crown. Then set the proper race setting tool (1.5", 1¼") fitting on top of it. Slide the extension piece down and into the setting tool, add your spacer coupling, then the main CRS-15 tool. Make sure each piece is seated and set-up properly and drive the race down on the fork crown by tapping the top striking surface of the CRS-15 with a hammer as you normally would. Done.