Spacers for Stronglight chainrings

amaferanga

I just put a 50 tooth Stronglight chainring on my 105 compact chainset. Didn't think about it beforehand, but as soon as I put it on I realised I needed some spacers (chain was catching the big ring when it was on the small ring and even the 4th biggest sprocket). I nipped to B&Q and got some. Had to hacksaw a chunk of each to get them to fit, but got them on and it seemed like they'd sorted it.

Anyway, shifting to the big ring is a bit rubbish now and at one point today the chain dropped between the two rings when I was changing down. So it looks like my spacers are a bit thick. Can anyone tell me what width spacers I need? The ones I have now are about 1.5mm so I guess I need either 0.6mm or 1.2mm.