1968 was the switch...thats what I have always heard,anyway..

Yes,drum keys are available...try ebay.uk for those.........$30-40 each!

Not sure when they swiched to square headed rods..........

A lot of people mistakenly refer to "metric" size. Pre-international size Premiers were sized in British inches, not metric, until sometime in the late 60s.

http://en.wikipedia.org/wiki/Inch

Royal Ace, you'll have to quote the relevent part of that Wiki article because I'm not seeing it. Seems to me the inch was standardised officially in 1959 but it was a pretty standard 25.4mm everywhere well before that. I have always understood the pre-international sizes were in fact metric and that if you convert them to metric terms they are exact sizes 12 = 30cm, 16 = 40cm and 20 = 50cm.

Calling Capt Wierd... He'll know.

1966 was the start of the change. During this time there was a lot of odd kits made with new sizes/parts and old parts. I'd say around 68 was the transition complete.

You're right absolutely.

They still had a lot of old OEM-shells in stock to beginning of 70's --- during that period there was a lot of deliveries to former Soviet Union --- a great part of kits had a mix from an old /new shells.

That is to say, "Hey, let you take all them cheap ! - we not need them anymore ..." :)

George.

Sort of makes sense for '12" pre-internationa'l and maybe 20", but '16" pre-international' are BIGGER than 16" and 40cm is LESS than 16"

Good point. So maybe just eccentric English sizing. Someone will know. And while you're at it, what's the thinking behind the Premier sliding washer design? It's kind of cool but I don't see any advantages of the sliding design.

Maybe the sliding washer made for speed of assembly or even a cost-saving in metal weight as these washers are very thin. They certainly help in taking the drum to bits as you do not have to fully take out the machine screws to get the part off