They are use to re-index the torsion bars.You can do the same by just turning the adjusting screw.If you need to turn them more than the screw allows,then something is wrong,and you will end up damaging something and severely affecting ride quality.
Save your money and just use the factory adjusting bolts.Put the money towards a set of Timbrens.
Joe- Buy a set of Torsion Bar keys from a K1500. They are the same parts for a fraction of the cost. I think the GM parts are around $26 each. They will only allow you to crank your torsion bars more, I don't reccomend them to anyone. However, in the case of supporting a heavy plow, they can be used to crank the torsion bars more, and then let back down in the spring, summer and fall, so that the front end components wear at the normal rate.
I hate to say this but honestly I would spend the extra
$10 and get a set of timbrens for your truck, the price difference is negligible and with the torsion bar cranked it will lead to fatigue and make it sag after a few years