The Brass gauge is used on the reluctor air gap on electronic ignition systems where non-ferrous blades are required. Metric and imperial. The feeler gauges are 83mm long Metric sizes: .038/.051/.063/.076/.102/.127/.152/.178/.203/.229/.254/.279/.305/.381/.406/.432/ .457/ .483/.508/.533/.559/.584/.610/.635/.660/.711/.762/.813/.889mm. Imperial Sizes: .0015/.002/.0025/.003/.004/.005/.006/.007/.008/.009/.010/.011/.012/.015/.016/ .017/.018/ .019/.020/.021/.022/.023/.024/.025/.026/.028/.030/.032/.035". Brass: 0.010"/.254mm