K4 US Screw and Plate, Longboard, US-Box

The K4 US Screw and Plate features an M4 stainless steel philips head bolt, while the plate is a brass insert moulded into tough nylon.

If your board uses a US-box / longboard fin bolt system, this K4 US Screw and Plate is a great alternative to the the usual stainless & brass US-Box bolt and nut.  

The M4 bolt is machined from stainless steel. Features a Philips head.

And the plate is a brass insert moulded into tough nylon.

Notes from K4

“These are HALF the weight of the original brass plates ones, which may not sound a lot, but this is a 20g saving in a quad. Add this to a set of K4 quad fins and there’s a saving of 0.2kg over a standard G10 set up – not insubstantial for the fins alone!

Strength-wise these are more than sufficient. A vice/lump hammer test showed the first failure was to shear the lugs off the back of the fin(!). Eventually with a good swing of the hammer the plate shattered destroying the brass insert along with it, but this was at a far greater load than you’d want to subject your board to even if you were hitting rocks.

I think we have a winner with these.”

Installation of the US-Box M4 fin bolt and plate

Slide the plate into the track of your us-box, put the screw through your fin and then screw bolt into the nut.  Tighten until hand tight...don't over tighten!

With this model, ensure you use the plate the correct way up…as per pictures.

It's worth while checking that it remains tight during and after use.

Also worth checking if you never remove the fin, that it is not seized into place...this is the same for any component used in open sea water.