Additional Options for 781B, 770B, 78 Bore Gages Spare Measuring Heads Spare Setting Rings Inreach Extensions for 770B, 781B, 781 Bore Gages Extensions from 2-1/2 - 6" can be added to both the 770BXT and 78XT, enabling internal measurements in deep hole bores (Multiple extensions can also be used). Internal Extensions Cat. No. EDP Ext. Size Fits Models Model Size in mm in mm 78/782F 65484 2.5 63 78XT/770BXT/781BXT–312-375 1/4-3/8 6-10 78/782G 65485 3 75 78XT/770BXT/781BXT–375-500 3/8-1/2 10-12.5 78/782H 65486 4 100 78XT/770BXT/781BXT–625-750 1/2-3/4 12.5-20 78/782J 65487 6 150 78XT/770BXT/781BXT–1 thru 2 3/4-2 20-50 78/782K 65488 6 150 78XT/770BXT/781BXT–2 thru 12 2-12 50-300 78-782J with 770BZ-2 Cat. No. EDP Range (in) HEAD100 73075 0.080-0.100 HEAD120 73078 0.100-0.120 HEAD160 73080 0.120-0.160 HEAD200 73082 0.160-0.200 HEAD250 73083 0.200-0.250 HEAD312 73085 1/4-5/16 HEAD375 73087 5/16-3/8 HEAD500 73090 3/8-1/2 HEAD625 73092 1/2-5/8 HEAD750 73094 5/8-3/4 HEAD1 73073 3/4-1.0 HEAD138 73079 1-1-3/8 HEAD2 73081 1-3/8-2 HEAD258 73084 2-2 5/8 HEAD314 73086 2-5/8-3-1/4 HEAD4 73088 3-1/4-4 HEAD5 73089 4.0-5.0 HEAD6 73091 5.0-6.0 HEAD7 73093 6.0-7.0 HEAD8 73095 7.0-8.0 HEAD9 73096 8.0-9.0 HEAD10 73074 9.0-10.0 HEAD11 73076 10.0-11.0 HEAD12 73077 11.0-12.0 Cat. No. EDP Range (in) RING100 73097 0.1000 RING160 73100 0.1600 RING200 73101 0.2000 RING312 73103 5/16 RING500 73106 1/2 RING750 73108 3/4 RING138 73099 1-3/8 RING258 73102 2-5/8 RING314 73104 3-1/4 RING5 73105 5 RING7 73107 7 RING9 73109 9 RING11 73098 11 RING9 RING5 HEAD250 HEAD2 HEAD4 211 starrett.com B ore G ages