Many thanks for all the replies and help folks. Yes it measures 19mm and weighs 4g so checks out as a half sov! He wouldn't have taken it out of circulation as he was born 1936 so I assume it was passed down from his mother. His collection consists mainly of British silver and some coppers, he has a small amount of foreign, mainly Commonwealth countries, but a crazy amount of sixpences, about 20 pre 1947 and over 100 post. I was wondering if there is a reference book or catalog for coins, like Stamp collectors refer to Stanley Gibbons Catalog is there an equivalent for coins? One thing I'd like to look up but cant seem to find from internet research (hence the need for a catalog) is if there was a time in young Queen Victoria's reign when they made coins with the heads and tails opposing? These five below all have the heads "upside down" to the tails, what was the time period this happened in? Many thanks again folks and apologies if the pictures come out massive, I can't seem to add them in to the post as before?