I had a Feridax lockable twist-grip in my box of spares but no key for it. I searched the net and found a discussion about changing the lock barrel on these jobbies. I discovered that the key number is stamped into the metal on the area where the two halves come together. I found a bloke on Ebay who sells these old vehicle type keys and ordered two for six pounds including postage. So, if I need to leave my bike I can now lock the throttle and the steering, plus add my meaty padlock and chain.