We always understood that the wood handle ones were issued for the tropics because the insect repellent simply melted the plastic handles and by the time you had brushed the sights clean the handle had stuck to your hands. The insect repellent was made by a chemical firm in Jockland called BAOchem. In Oz, we said it stood for Britains Agent Orange. To be honest, the blanket stackers at Ordnance in Singapore didn't care what they sent out