Originally posted by jatrax
Second there was someone who made a set with contacts, I forget the same, if you do a search on the forum you might find it, but they are very rare and expensive, only source would be ebay or maybe KEH.
At the very least you have two variations with contacts - the ones made by Kenko (and sold under it or a related brand) and a different, somewhat flimsy (but good enough) set like I have. Mine is branded as "PANAGOR" - I believe it was also sold as Jessop's house brand, and possibly under other labels as well. It has 31, 21, and 13mm "PKA/AF" tubes. They're actually MF, but the contacts work. IMO you should take whatever brand you can find, as long as it's in good condition.
I also have the Pentax tubes ("ASAHI PENTAX JAPAN") which are better made. They have no contacts, but they do have an aperture lever, and they work well within this limitation. I much prefer their construction, but ultimately, I think the contacts matter more. However, for a while I couldn't find ones with contacts, so I bought them. They're much better than the cheap no-names on eBay with no contacts.
These two look like they're identical to my ASAHI PENTAX set:
http://www.ebay.com/itm/Asahi-Pentax-Auto-Extension-Tubes-Set-of-3-Tubes-P-K...item3f1ace45ff http://www.ebay.com/itm/PENTAX-AUTO-EXTENSION-TUBE-K-SET-MINT-IN-BOX-/400318...item5d34d3666d