Heads for assembly with measuring or machine tools. Three types, thimble diameters below 1 in, 1 in and below 2 in, 2 in and over; measuring ranges ½ in, 1 in, 13 mm, 25 mm. Material, micrometer screw, spindle, thimble and barrel adjustments, measuring faces and graduations, dimensions and standards of accuracy.Cross References:BS 817BS 818BS 852BS 863BS 869BS 870BS 887BS 888BS 906BS 907BS 939BS 957BS 958BS 959BS 1054BS 1643BS 1685BS 1790