This is a set of long cylinder head nuts, they help to keep the Lambretta cylinder head torqued town nice and tight, saving air leaks and holed pistons! Made from zinc plated mild steel. 
 
Size approx: 24mm long, these are slightly shorter than the long, traditional cylinder head cowl bolt, hence the reason for the other listing selling just 3.
 
Pack of 4. Ideal to use on the Ron Moss Avanti or A.F. Rayspeed mammouth cylinder heads, giving perfect balance to the head cowling. 
 
4th picture shows the size of he nut compared to a standard M8 nut.