Roly, was it this thing:
They cost about £18 from the place which supplied me with the hardware kit to unbugger my Weber,
http://www.supergreenthumb.com
They also provide spare bits for gas gays.
On a totally different note, to petrolheads of a certain age, 'Weber' means twin fortys! As in 2 x 40DCOE carbs, the RR of bolt-on performance before the days of chavs 'n chips!