ナベ小ねじ - nabeko neji
Pan Head is the principal variety of screw found on Japanese motorcycles. Pan head were used almost excusively for engine cranckases until the mid 1980s. Easy to mess because you don't have the right screwdrivers and often replaced by much better but ugly Allen bolts!
Exact replacement for these OEM reference famillies:
Honda: 93500-xxxxx
Yamaha: 98580-xxxxx or 97885-xxxxx
Suzuki: 02120-xxxxx
Kawazaki: 220B-xxxx or 220AA-xxxxxx
Japanese vintage motorcycles, JIS screw, small head nut, small head bolt, pan head screw, honda, Kawasaki, Yamaha, Suzuki, Kawasaki 900 Z1, honda 750 CB K, Yamaha 350 rd, Suzuki 750 gt, zinc, stainless, acorn nut, black zinc, Japanese industrial standard, JIS screwdriver, engine bolt, flange bolt
JIS Screw Pan Head
Zinc is now called trivalent plating treatment which is a modern plating that looks similar to zinc without the chemical hazard and better consistency and corrosion resistance. This is the standard for Japanese manufacture and I recommend it for a perfect restoration.
Black aspect trivalent plating treatment which is a modern plating that looks similar to black zinc without the chemical hazard and better consistency and corrosion resistance. This replaces black zinc of early models and is now standard for Japanese manufacturers.
Yellow chromate treatment is a plating often found on small screws for carburetor or to give a rich aspect. Widely used in the 70s it has been replaced by trivalent zinc because of its environmental hazard.
Chrome platting is used for a beautiful mirror finish. However it is used only for very visible bolts, never seen for screws. Acorn nuts should have this chrome platting for a perfect reflection. If you like a highly polished look this is the finish to use.
Stainless is not a plating but an alloy of steel made of iron and containing 12% Chromium in JIS screws. It is resistant to rust and corrosion so the aspect never changes. Disadvantages are mainly the price of stainless steel fasteners and the risk of galling when threaded into aluminum engine casing. A lubricant is highly recommended.