Ring gages used to check external thread, plug gages used to check internal thread. GO & NOGO, RH(right hand) & LH(left hand) available Standard tolerance: Plug 6H & ring 6g, if no special note, ring gage 6g, plug gage 6H will be choosed. Plug gauge thread class: 4H,5G,5H,6G,6H,7G,7H Ring gauge thread class: 4h,5g,5h,6g,6h,6e, 7h All these ISO metric thread gauges are made according to standard ISO1502. ADD TO CART