Unlike in larger scales there seem to be few 2mm scale layouts with working 3-link couplings, and perhaps with good reason. They are small and fiddly - probably not a realistic option where shunting, ie regular coupling / uncoupling is required. (An association member has been working on a neat method that gets round this problem using magnets).
But other coupling systems don’t quite reproduce that concertina effect as a train slowly starts or stops. And since shunting isn’t a great interest for me, I like to use 3-links where I can.
A hook and a chain aren't difficult to fit. Some of the Association wagon kits include the hooks, others need to be adapted:
Slit cut with a fine saw.
I find this style of hook easy to use, as there is a small opening behind the hook, making it easy to insert the chain.
I've blackened the links with Gunmetal Blue. They come from a necklace chain purchased for this purpose. (Don’t know what the jewellers’ assistant thought about my concern with the length and shape of the links, but she was very professional).
With a dab of epoxy behind the solebar and the link fitted behind the hook, the hook can be slid into place.
