The inserts are machined from cast iron... damned hard to cut. Explains why they tend to crack over time, too - - cast iron is not malleable, and will crack rather than bend. Pretty well finished off my hacksaw blade cutting that insert to length; about haalf the teeth gave up in the process.

The cracks around the base of my back-up insert let go when I dropped it on the workbench after cutting it. I was able to snap it back together, and it's unlikely to fall apart once installed, but it may leak a small bit.

Anyone know if cast iron can be gas welded? I may want to take this somehwere to be weleded up, but don't want a heavy bead added to the thickness.