I want to put some bolts in the ends for the legs to sit on, but don't know what screws to buy for it.

Thanks in advance,

These holes are designed to be tapped to fit a 5/16-18 thread as are all of the other 15 series components. The 10 series are designed to be tapped to fit 1/4-20 fasteners.

Hope this helps.

Dan

Hack's info on the end taps is right on. If you need to fasten a joining plate to the extrusion, take a look at 5/16-18 Carriage bolts. The square shoulder fits nice and snug into the t-slot and they are far cheaper than the 80/20 fasteners.