10p Thick Covers 1976
10p Non-Pictorial Stamps 1976 - 1977
These were Experimental Booklets designed to fit in Vending Machines.
Many booklets had different margin perforation, thick covers and in some Lavender (Pale Blue) Missing.
Combination of Thick Cover and P1 Perforation are scarce and demand higher price.
The Booklets varieties came from Stoneham (STN) and Machin Collectors Club (MCC) Catalogues.
These two Catalogoes went deeper into the varieties of Perforation Types, Cover thickness etc.