This is a spacer manufactured from aircraft quality T6 aluminium to fit the Triumph pre-unit long primary chaincases pre-alternator models. The Primary chaincase has a tear-drop shape towards the front. The early clutches were fitted with only 5 friction plates and a shallow clutch basket/sprocket. If you need or want to update your clutch to take the 6 plates, fit the 7 plate clutch conversion or indeed fit a clutch belt drive conversion then the primary chaincase will not be wide/deep enough. We have therefore had these spacers manufactured to space out the primary chaincase. The fit is correct. You will need slightly longer screws. The spacer is 1/4 inch deep.