What Tufnol is
Tufnol is a brand of laminated thermosetting composite — layers of woven cotton fabric, paper, or glass cloth impregnated with phenolic or epoxy resin and cured under heat and pressure into a rigid sheet, rod or tube. The lamination gives it a useful combination of properties that plain plastics or metals don't match on their own: good mechanical strength and dimensional stability, electrical insulation, and resistance to a range of chemicals and to wear, all in a material that machines cleanly on standard workshop equipment.
Why grade selection matters
Different Tufnol grades are built around different base materials and resins, and the grade determines what the material is actually good at — a cotton-fabric/phenolic grade favours mechanical strength and machinability for gears and bearings, while a glass-cloth grade trades some of that for higher strength and better performance at elevated temperature or in more demanding electrical-insulation duty. Specifying "Tufnol" alone without a grade is roughly equivalent to specifying "steel" without an alloy — the grade is where the actual engineering properties live.
Common applications
In industrial and electrical work, laminated plastics of this kind commonly turn up as electrical insulating boards and formers, gears and bearings in lightly-loaded mechanical assemblies, jigs and fixtures, and general-purpose engineering components where a machinable, non-conductive, dimensionally stable material is needed in place of metal. When specifying a replacement or a new part, matching the original grade — or at least the property it was chosen for (electrical, mechanical, or thermal) — is more important than matching the brand name alone.