Hi elenhinan

I've had a similar problem when trying to buy from several ebay suppliers too, I've found it best to buy both screw and nut from the same supply company to ensure a match. Having said that, if you buy from a company based in your locale there shouldn't be so much trouble or expence if they send you the wrong thing, but you'll certainly be paying more for it.

There's a lot of 16mm ballscrews with antibacklash nuts for sale on ebay from our Chinese friends at not a lot more cost than local trapizoidal screws, it's worth a thought and some will even machine the ends to your specification if you ask nicely.

I use Trantorque keyless bushings to locate and lock my timing pulleys, they require a 26mm x 10mm stub on the BK12 end, though the standard BK12 end machining is a 15mm x 10mm stub, the extra charge was only a few dollars and actually cheaper than getting a woodruff key slot cut over here in the UK.

Happy hunting

Graham