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Originally posted by robthebloke 
To be honest, why are you even bothering to do this?
You can buy a very cheap generic set of K-mount extension tubes for just a few quid on eBay. They're unlikely to have 'A' contacts, but then your teleconverter doesn't either. You can purchase the Kooka 25mm extension tube with AF and A contacts brand new if you really want (I have one, I'd only recommend it for DA lenses with quick shift to be honest - the additional gearing when trying to manually focus an AF lens is a little disturbing!)
The very cheap extension tubes from China are just that, cheap. They are 5 parts which are screwed together (just barely tightened) to form a long extension tube which aligns with the lens' focus hashmark - once. God help you if you start tightening the tubes tightly together, then the lens may even end up upside down. If you loosen off the screwed parts to maintain the tubes' alignment with the lens hashmark, the tubes start to wobble and no longer feels too safe to use. It's much better to get a dedicated extension tube set like the Vivitar AT-22 or exponentially more expensive AT-23 with contacts or if you have old K-mount 2x TCs, de-glass them as OP was asking. I've de-glassed 3 2x TCs and I was fortunate enough to acquire the AT-23, which came as a part of a camera bundle that I purchased a few years ago.
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