Summary

The iron holder that came with my Hakko FX-951 station appears to have room for a roll of solder but includes no parts to do so.

This thing is basically just a pipe to support a spool of solder and let it spin freely. Inner diameter 6.6mm, outer diameter 18mm, 73.4mm long. It's held in place with a piece of threaded rod and a nut on each side.

The tip of the iron sits about 15mm above the solder spool, which might be uncomfortable for some but I've had no issues.