M4 Thin type nylon insert lock nut. A4 grade stainless steel Nyloc Type d = 7.66 mm h = 5 mm m = 2.9 mm s = 7 mm thread pitch = 0.7 mm Nylon insert can be various colours. Please ask if colour is important to you A4 grade stainless steel has a greater corrosion resistance than A2 in certain environments. It is often used for Marine applications especially when coming into direct contact with salt water DIN985