18G39 - Clutch plate cenralizer.
This tool is used when bolting the clutch cover assembly to the flywheel to centralize the driven plate. It ensures that when fitting the gearbox to the engine that the first motion shaft passes easily through the clutch driven plate hub and locates in the spigot bearing in the end of the crankshaft. Mentioned in Section E of the MGA Twin Cam Workshop Manual.

18G276 - Clutch plate centralizer. - (not shown)
Alignment pilot tool for centering clutch disk on flywheel when installing the driven plate assembly. Mentioned in Section E.6 of the MGA Workshop Manual.

18G279 - Clutch plate centralizer.
When assembling the single plate clutch it is essential to use this tool to assure that the clutch plate is concentric with the spigot bearing in the flywheel centre, otherwise it is impossible to assemble the gearbox to the engine. This tool wil also fit the Wolseley Four-Fifty, Morris Oxford (Series MO), And Morris Six (Series MS) models. Mentioned in Section Q of the MGA Workshop Manual.

Cheap modern plastic tool works well.