This is a 1/4" diameter 4" long Reactor Rod for GEET, plus two 4" stop rods. Rod has small bumps on both ends, to center it inside 3/8" OD pipe with about 0.03" walls. If the wall is thicker than that, you may need to fille the bumps off a bit to make it fit. Also has a dimple on one end.
Pick one for high temperature, made of steel or gold-plated or antique bronze, or even a silver one to experiment with.
For expeimental use only. For commercial applications you may need to get a license.