In article , N_Cook
says...
No tools it said - what a clever idea I thought.
Not unless you have the fingers of a rock climber , or what is the secret.
One thing I learnt long, long ago , tie a bit of wire a few links back
either side of the link before removing or replacing to take the tension off
the link area.

With these links the only way I could put one end on the pin and then just
preliminary place the other one was to put a bit of a set in that closure
link, so it would slide over the top of the second pin when firmly pushed by
finger.
Then 2 pairs of molegrips, not particularly firmly gripping but enough to be
able to flex the made-bridge piece enough to complete the locked closure.

Eh? All you do is hold the chain on each side with your fingers, press
with your thumbs and pull with your fingers to flex the chain, and
wiggle/pop the front plate over the pins with your thumbs. Then flex
the chain a bit the other way to make sure the plate is fully engaged in
the slots on the pins.