Roof bar problem

Just wondering if anyone has experienced the same aggravation as I'm having with roof bars and cycle racks?

I bought these eBay aero bars for my Mazda 6 estate:

http://www.ebay.co.uk/itm/121625432202?_trksid=p2057872.m2749.l2649&ssPageName=STRK%3AMEBIDX%3AIT

And I then bought the Exodus 1 bike rack from Halfords:

http://www.halfords.com/motoring-travel/roof-bars-boxes-bike-racks/roof-mounted-bike-racks/exodus-roof-mount-cycle-carrier

After fitting the roof bars, I then went to fit the cycle rack but the T-Track adapters with the rack are 20mm and the T-Track on my roof bars are only 15mm

A quick mooch online leads me to the conclusion that almost every other roof bar has a 20mm T track so why have my bars only got 15mm? :wall:

Anyway, I can't seem to find a 15mm T Track adapter so I guess it's back to Halfords and buy a proper set of Exodus roof bars for £85 more than the eBay bars.

Does anyone have any alternative solutions? What do you use on your roof?