Tool to use with a DeWalt cordless grinder (DCG414 in my case). The grinder comes with an Allen Key to open the clamp, which I find a little light on. This tool uses 2 x 6mm Allen Key bits to engage the grinder clamp and get better purchase.
(2) 6mm by 1/4" Allen Key hex bits
You could also use ABS. Not sure that PLA would be a good choice but might be worth a go.
Insert bits into printed spanner
The bits are a size for size fit, so take some tapping in to fit but we're looking for a firm fit here - it's not hard. Tap them through until about 2 or 3mm protrude through