I believe the casting process is the reason for all core plugs of whatever ilk surely? My point being that "commercial" drive-in and expand types et al do not "freeze-out", invariably the block goes first.

Along the same lines see also those devices known as Eze-outs, or easy-outs to us; they are never easy or out, and I am convinced they are designed by the Snap-off Tool Co. in conjunction with the World Federation of Spark Eroders.

In another case of brain going faster than fingers and short term memory of a goldfish, I did mean the B61 was never in production for British MVs, although was used in several civilian applications.

There are certainly a number of ways to get those eclipsed head nuts torqued down, starting from a feel-calibrated right arm with a shortish ring spanner to special tools, whatever.

R.