3/4 caps wouldn't go onto the radiator to carry it outside, he probably means 1/2 plugs ( brass, galv or black iron)
The 3/4 caps are useful for putting on the radiator valve, type with bigger nut 3/4 , just in case someone accidentally opened the valve when the rad is removed.
Something to catch the water in after undoing the nuts would be useful :thumbsup:
One of the worst things about removing an old radiator is the black sludge that sits in the bottom of some.