Profile: The George H. Seltzer & Company manufactures and stocks ZIP machine tool accessories in English (inch) sizes. We can also provide metric sizes on request. Our primary product is the ZIP machine table T-slot bolt. They are hot forged from C-1045 steel in diameters from 3/8" to 1". Our product line covers T-slot bolts, hex nuts, flat washers, T-slot nuts, steel wedges, plain strap clamps, goose neck clamps, four-sided step blocks, and extension nuts. ZIP machine table T-slot bolts are hot forged from C-1045 steel. These are especially made for machine tool tables. Bolts can be heat treated to grade 5. ZIP extension nuts are all machined from 12L14 cold finished hex bar stock. These are used as a coupling nut with studs to lengthen bolts.