My new high volume water pump came with a cylindrical small slug, about an inch long and 3/8" in diameter. No instructions as to what it is for. Anyone know?

is it threaded?

No, smooth and slightly tapered at both ends. Maybe I'll just drop it in the radiator :)

Possibly a plug to eliminate the bypass?

Possibly a plug to eliminate the bypass?

DittO: hole on pass side , below the main water outlet.

DittO: hole on pass side , below the main water outlet.

I appreciate the responses but the plug diameter is just slightly smaller than the bypass diameter. It fits but slide loosely. If I tried to install, I think it would have the same effect as dropping it in the radiator. :)