Most of the Euro torque wrenches (Hazet, Stahlwille, Gedore, Facom, etc.) are designed with modular heads on a rectangular drive like 9x12 or 14x18. That way, you can directly switch between a ratchet head, fixed square drive, ring spanner, open end wrench, flare nut, etc. You can also get blank attachments intended for welding or custom machining your own special tooling (ex: you need to torque something with a triangular key or a pin spanner for a special application). The other neat part is that if a ratchet head breaks or you want to upgrade to a higher tooth count or a quick release, it's easy to do that. The only real downside is that the full sets tend to be pricey and the design doesn't really allow for flex heads.
Here's an example of a Hazet "master set":
Buy online at the best price: HAZET 6290-1CT/29 Set of torque wrench with insert square and inserts (29 pcs.). Discover Torque wrench and accessory sets by HAZET for sale on Mister Worker™. Fast delivery and Custom Quotes.
www.misterworker.com
Because of the ecosystem for all of that stuff, torque adapters like on US fixed head torque wrenches aren't as big of a deal. I know Stahlwille has a limited selection but I'm not sure who else besides that.
If you just want a cheap one in general, Sunex makes a set which is rebranded a bunch (I know Cornwell for sure but probably Matco and Carlyle/Napa too).
For a motorcycle application, I'm assuming it's probably something like the nuts at the base of an air-cooled cylinder where there fins overhang the fastener?
I have this thing, which although not super pretty, does work and fits whatever size wrench you might need as long as there is clearance:
Motion Pro - High quality cables, tools and controls for motorcycles, ATVs, snowmobiles and personal watercraft.
www.motionpro.com
www.misterworker.com
www.mactools.com
these are on ebay from sealey tools £149
