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A fret of enough instanta couplings for nine 4mm scale wagons.
These have been tested and found to be robust enough for most normal modelling situations. The design incorporates a collar that can either hold the coupling tight against the wagon headstock or be fitted with a small spring to minimise shocks.
There may be residual wax support material on these parts, and they should be washed in hot soapy water to remove it and free up any sticking links. They can be coloured with acrylic paint or felt tipped pen.