O-ring to replace hop unit spring size?

[L33]

Hi all
I know a potentially better way of ensuring the hop unit pushes back against the gearbox is to slip O-rings over the inner barrel in front of the hop unit. Does anybody know what size (inner & outer diameter) these need to be?
I've had a good search but can only find reference to US o-ring sizes.

If it makes any difference this is for an M4 hop unit, G&P body, Madbull inner barrel.

Thanks!

[Sidewinderforge]

Re: O-ring to replace hop unit spring size?

Given Airsoft inners are 8-8.5mm OD and Hops are about 12mm dia where the barrel goes in, this took me 30seconds to google: http://www.ebay.co.uk/itm/8mm-x-2mm-...item1e86cf8214

[L33]

Re: O-ring to replace hop unit spring size?

Thank you, appreciate it.

[CJC]

Re: O-ring to replace hop unit spring size?

I use the 8mm x 2mm and they work well