A round peg may not be best to put into a square hole. It could fit into a hole bigger than it, or with enough force, into a smaller hole, but it's not the right fit, the hole should have a square peg that fits correctly. Evaluating both your task and what your tool is able to do is needed before attempting it. If you're going to put things together yourself, try for a jewel bearing situation, where everything fits nicely, peg-to-hole, with as little friction as possible.