Manfrotto 030-38 Hexagonal Plate 3/8

As with most Manfrotto kit, it's a well engineered and constructed piece of kit. However, it's not perfect. Unlike the smaller, oblong plates, it's slightly more tricky to tighten sufficiently.

If, like me you were that 7 stone weakling that didn't answer Charles Atlas' invitiation on the back of your comic all those years ago, this may help:

My favoured method is using one of those little elongated "S" shaped allen keys normally found in flat pack furniture supplied by that well...