Re: C100WM10 – Currys pulley bolt size
TBH anyone attempting to do repairs should have a decent set of tools to start with, covering most of the common spanner, socket sizes. Basic socket sets are cheap as chips at B&Q etc.
Off the top of my head I could not tell you what size of bolt was used in the vast majority of machines without looking at it or trying the tools at my disposal.
You should use nutlock on the threads but in some cases even that is not enough to stop the bolt from coming loose again .