If you've ever changed a chainring on a crankset yourself, you'll know this can be an awkward task. You have to use an allen wrench plus a separate wrench for the slotted bolt on the opposite side. For tightening, while you can position the back wrench so it holds against one of the crank arms, it can be tricky since there's nothing to hold the back wrench in place against the slotted bolt. If you're not careful when tightening, you can easily cut yourself, especially if you try to tighten the allen key
towards the chainring teeth. VAR in France used to make a tool for this that makes installing or removing chainrings easier…and with less bleeding, the VAR #352.
I recently acquired a vintage version of one of these. Though the way it's made may be slightly crude by today's standards, the VAR 352 is a cleverly designed tool, complete with a spring loaded arm that holds the built-in allen key in place.
Merci VAR
