This back cap is compatible with 20, 20H-320, 9, A-125, PTA-9, PTW-20, W-250, W-280, W-375, 20FHD, 20H-320-25R, 20P, 25, 9, 9F, 9FVB, 9 HP, 9P, 9V, 9VB, PTA-9, PTA-9F, PTW-20, WP-20, WP-20V, WP-9, WP-9F, WP-9FV, WP-9V, WP-R9F, WP-R9FV, WeldTec brand and is for use with A-125 Series, W-250 Series. It can be used for TIG welding.