Hex plug gauge 6.35 MM A/F, Hex. Plug Reversible double sided GO Gauge -6.350 to 6.354 A/F - GO Depth 4.759 to 4.765, Nogo Depth 5.035 to 5.050 mm (Required to check The HEX Slot For I0543.00 Atlas HFN BOLT HPG6350.6426.4750.5050)