MGA (and many other vintage Bitish cars) use an analog temperature gauge with a sensor bulb filled with ether to generate vapor pressure to operate the gauge. The sensor bulb fits into the cylinder head and is sealed on the under side tapered surface of a flange that is part of the bulb. It is secured with a tube nut that screws into the cylinder head. A problem arises with many modern replacement rype temperature gauges where the threaded tube nut is too short, resulting in the hex part bottoming out on the head before the bulb is sealed on the flange. The hand made shim is abit of a fiddle, and it might be lost during subsequent future servicing.

A commom solution is to make a thick horseshoe shim to fit between the nut and the bulb to effectively exend the reach of the nut. A better solution is to install an adapter which was used on Austin Healey Sprite and MG Midget 1968-1974, and Morris Minor 1952-1972. This fitting screws into the cylinder head using a copper washer for sealing. The female thread of the adapter is shorter to allow use of the shorter flare nut (without need for shimming). Adapter part numbers: 11K2846 (BMC), 361-065 (Moss Motors USA). Copper sealing washer AED172 (BMC), 324-805 (Moss Motors USA)