Legs and Levelers
The most common way to have leg levelers are to make the legs from 2 x 2's and drill a hole large enough to except a "T" nut and 1/4" x 20 x 3" carriage bolt. This idea has several problems.
The first is that the 2 x 2's can warp or twist if the wood has not been properly cured and dried. Second, if the hole in the bottom of the 2x2 is not drilled perfectly perpendicular to the bottom of the leg then the carriage bolt will rub on the interior wall as the bolt gets turned in further. Third, as the modules get moved around, the drive-in "T" nut becomes loose and will eventually fall out, making the setup a virtual headache.
To overcome these problems we started out by making the legs in an "L" shape configuration, this "L" shape seems to resist the twisting and warping that's encountered with the 2x2 legs if the wood has not been properly dried or cured. From a common pine 1 x 4" (actual size 3/4" x 3 1/2"), rip two strips of wood, one 2" wide and the other 1 1/4" wide, then assemble these pieces together with glue and screws to form an "L" that measures 2" x 2" on the outer dimensions. Then we attach a piece of hard wood i.e.: oak or maple, to the bottom and inside of the of the legs. This block measures 2 1/2" tall by 1 1/4" square.
Being only 2 1/2" tall, this allows the block to set flat on a drill press base and ensures a straighter hole that is perpendicular to the bottom of the block. The hole should then be drilled completely through the block ( a bit larger than the diameter of the "T" nut ) so that the carriage bolt, when fully turned in, will protrude out of the top of the block. Then the block can be attached to the leg, the bottom of the block being flush with the bottom of the leg. When you attach the block it's a good idea to glue it and either nail or screw in place, being careful not to let the nails or screws enter the hole for the leveling bolt as this will hinder you from threading the bolt through completely. This might be a good time to make mention to offset the hole to one corner of the block. This just gives you a little more room to nail or screw it on.
We use a 5/16" "T" nut and carriage bolt for our levelers. These seem to resist the bending that affects the thinner 1/4" bolts. The "T" nuts do not drive-in like the normal "T" nuts do, instead they have three holes in the plate which we use screws to attach them to the bottom of the blocks. Since the blocks are made from hardwood the screws will hold better than if attached to a softer wood . You may need to enlarge the holes to accept larger screws and may have to drill pilot holes in order to drive the screws in easily.
The completed legs can then be attached to the module framework in the same manner as the normal 2 x 2 legs are. With these simple modifications to your legs, you should experience years of trouble free leveling!