40mm barbed staples are a very popular product in the agricultural world.
They effectively secure line wire and many types of mesh and net fencing to timber posts. The two sharp end are driven into the post over the wire.
The sharp barbs anchor the 40mm barbed staples into the timber, preventing them being pulled out if pressure is applied to the wire being secured.

These 40mm x 4mm galvanised Staples come in a 1kg Bag.