The Vajra as Implement, Emblem and Symbol

"To briefly summarize, we may say that while the Vedic Vajra weapon seems to have had a form of some kind of club or axe with an attached handle, the Buddhist Vajra has its particular form because of influence, at some as yet not precisely specified time, by way of the Middle East, or very possibly by Greeks residing in areas to the northwest of India. "

http://tibeto-logic.blogspot.co.uk/2012/04/vajra-as-implement-emblem-and-symbol.html