Just received a new 42t chain ring. Dropping the ratio slightly from 49/20 to 42/18.

I have a Park Tool chainring spanner to hold the slotted nut at the back. I've only had to use it a couple of times in the past (I don't change chainrings often!) and it was a very poor fit and chewed at the edges of the slot.

I've managed to get it "tight enough for now" but I've also ordered a new set of chainring bolts.

What is the best tool for holding the slotted nut? I normally find Park Tools pretty good but this particular tool is just a piece of pressed steel that is barely an approximate fit.

One that's available in the UK would be ideal!

Thanks.

I've never had trouble with the Park tool, but maybe try the Shimano TLFC-22.

I use a chainring bolt tool and hold press it into the slots with a vice grip so it doesn't slip. Eliminates the bolt slipping and rounding out the edge.

All sorted. Thanks to those who replied.

The old chainring bolts were good few years old and the threads were a bit graunchy even after I cleaned them. They may also have been a tiny tad too long for the new chainring, even though it is for a single speed. The Park Tool spanner was a very poor fit for them.

New chainring bolts arrived today, courtesy of Amazon. The threads were smooth, they were a tiny tad shorter, and the Park Tool fitted the slot perfectly. A triple whammy! They went in easily and nipped up with no trouble at all.

Bike is now on 42/18 which is 63 inches. Before, it was on 49 x 20 which is 66 inches, and I now have the 20t in reserve if I want to do some serious off roading when the mud has dried up a bit.

63 inches is pretty low, but I've found in recent rides that I wanted a "slightly lower gear" more often (headwinds, long gradual climbs) than I needed a "slightly higher gear" (the very occasional hilarious descent).