High quality internal tooth starlock washers assortment sets ,good for quick fixes and make a repair very simple.mainly use for appliances, lawnmower,motors, tools, cars, trucks, trailers, electronic equipment, toys, bikes, RVs, boats, pumps, furniture etc.Working principle , a lock washer exerts a spring force between the fasteners head and the substrate, which maintains the washer hard against the substrate and the bolt thread hard against the nut or substrate thread, creating more friction and resistance to rotation.Made of 65Mn metal steel black oxide finish,no burr ,providing the good resistance to corrosion and high temperature.7 most-used size types M3 M4 M5 M6 M8 M10 M12 for the handyman, professionals, industry, craftsmen and do-it-yourself people, good compatibility.Total 280 pcs come with transparent plastic case for sorting and storage .