ceramic or carbon/graphite weld spacers

It used to be the when weld repairing automotive crankshaft journals etc, before welding began "
> carbon/graphite woodruff keys would be inserted in the keyways on the crankshaft snout
> carbon or graphite rods would be inserted in the oil holes

The purpose was to keep the original crankshaft features open and clear of the weld applied continuously around the journal or snout.

Sometimes "ceramic paste" is mentioned as being used for the same purpose.

Does anyone know proper technical names for the materials used ?

thanks,

Dan T