SU starting carburettor electric solenoid type . Model SU 3256 LL , the LL probably means Low Level. The Brass Nut shown is only for illustration to show the fine thread is fairly good , the nut screws in and out by hand , thread was lightly oiled. The bowl appears to have a replacement threaded bolt to replace the original at sometime . So offering  for spares or renovation/restoration. The bowl lid has no parts to it just the bare lid.