Many components and accessories of Transformers toys must have an way to temporarily attach to each other, and the means used must be simple, cheap, and easily detachable. Very often the chosen solution is a friction peg and peghole. Weapon handles and the fist holes they plug into are often made this way.
The peg, a fraction larger than the hole, deforms itself and the hole slightly as the two are pushed into engagement. Since all solids are somewhat elastic and act as springs if not overstressed, the peg and hole press against each other, causing friction that prevents the parts from slipping easily apart.
Transformers toys use several standard peg and hole sizes. In recent years, a 5-millimeter diameter has been particularly common, to allow for interchangeability of accessories between toys. The Mini-Con Powerlinx "hardpoints" of Armada and later lines are 5-millimeter pegs with a 2-millimeter hole drilled in the center; on "live" hardpoints, the hole has a tiny plastic "trigger" peg inside that activates a spring-loaded gimmick when pushed down by the peg within a Mini-Con's Powerlinx socket.