According to the valve museum this was introduced in 1959.  However interestingly this valve has the date 1.7.53 painted on the top of the valve (see image).  There is more writing on the top:

"SO 3267" and I have no idea what that means...

On the side is printed Z 729

Beneath this:

"JF" on the left and

"3" on the right

For international buyers: Please note this will be shipped via ebay's Global Shipping programme.  This means that I am unable to alter the price of shipping before or after you buy it.  Also unfortunately ebay does not allow for combined postage using this method.