Thread connectors are used to join 2 pieces of threaded material together where a longer fixing is not available or suitable. Most commonly used to join lenghts of threaded bar together to make longer lengths than are widely available, they can be used with almost any fastener.
The length of a threaded connector can usually be found by multiplying the thread diameter by 3.
Zinc coatings prevent oxidation of the protected metal to create a longer lasting finish. It does this by forming a barrier and by acting as a sacrificial anode if this barrier is damaged. Zinc oxide is a fine white dust that (in contrast to iron oxide) does not trigger a breakdown of the substrates surface integrity as it is formed. The zinc oxide, if left intact, can act as a barrier to further oxidation, in a way similar to the protection afforded to aluminium and stainless steels by their oxide layers.