ntxt

I can't give the technical explanation, but if you can get a copy of the 1984 Gun Digest and read the article by Jack Lott on Stopping Rifle Stocks. A great read and will explain a lot.

its not compression.. that would cause the wood to warp badly.
It is mechincal, to keep the wood from "accordianing" .. expanding outward.

you can also use the front one to have the action tang have a boarder place to hold on.

imho, the rear xbolt is more important.
jeffe

G.Hansen,
These hidden crossbolts of steel all-thread may be 1/8", 1/4", 3/8" or even up to 1/2" when buried behind the primary action recoil lug. They are buried in epoxy, and the adherence of the wood to the epoxy and the unyielding steel crossbolt will indeed reinforce the stock, and probably better than the compression of a spindly screw-together exposed crossbolt, unless that exposed crossbolt is also epoxied in place in the unexposed internal setting of its shaft.

The hidden crossbolt between the trigger well and magazine box well is more limited in the diameter that it may be, but it is similarly effective due to the epoxy adherence between steel and stock wood.