Extendable bike steerer/fork dummy tool

Inspired by Dave Rome's tool from this escape collective article, but this tool allows you to thread extensions on for short printers or long head tubes.

This tool is used to hold the stem and any bearings, spacers, or other pieces in place while the steerer tube is removed.

You can slide this down from the top to hold bearings and stem in place while a fork is removed.  But you can also slide this up from the bottom after the fork is removed to hold everything (including the bottom bearing) in place while your fork is removed.  When doing this, use your stem to hold the steerer in place.

If you only need 160mm, you can just use the top piece.  If you need longer, you can add 135mm or 75mm with the extension parts. 

All parts should print as is with no supports required.

Depending on your bed adhesion, you may want to put a brim on the extension part.

4/2/2023
Added a bottom stop to thread on to keep any lower headset pieces in place
fixed threads not going all the way through on extensions