These three 12 X 1.25mm stainless steel cap nuts fit:

WA20K1 C WATER PUMP

WA20K1 D WATER PUMP

WA20X C WATER PUMP

WA30 C WATER PUMP

WA30 D WATER PUMP

WA30X C WATER PUMP

Not in original packaging  

If you rebuild or restore any type of machine you know how important it is to use genuine / original factory parts when possible. A repair or restoration is intended to return that project to as close to original as possible, right down to the stainless steel cap nuts.

If there's even a chance you'll need this/these replacement part(s) in the future you'd better get them NOW!. Keep this in mind,  replacement parts are always good to have. When you decide to sell your Honda, including a few extra replacement parts always sweetens the deal for both buyer and seller.