I can't bring myself to pay £25+p&p for a length of tube with some flats machined on and a couple of pegs, when I work over an engineering factory. Seems like something that could be knocked up in 10 minutes or so... I note that they're for sale in the US for $10 or so, but over here it's £25+
If anyone has one to hand and can give me some dimensions, the length (Although I imagine I could work that out by the length of the handguard), width of the prongs at the barrel nut end, and OD of the tube used, that would be great...

