This item is called a thru-hull or sometimes a "mushroom head". They are straight threaded (NPS thread) so they can be cut to the correct length for your hulls thickness and then be threaded into a female straight threaded seacock or a flanged adapter. The one on the right has already been cut to length. Most all thru-huls installed into proper seacocks will need to be cut to the proper length.


When installing them with a proper seacock the nuts are not used.


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