Need info on steel clasp size for pilot watches:

I have a Ceramic Fliegerchrono ref. 3705 and decided to wear it on a black NATO nylon strap. Lug width is 20 mm. I was trying to order a 20 mm steel clasp (pilot style), not the folding claps. AD told me that according to his knowledge the maximal size of the pilot clasp is 18 mm. Any info on the existence or non-existence of this clasp? If exists, an ordering number is also welcome.
Thank you, best regards:
Robert

The tang buckle from my 3706 is certainly

18mm as is the folding clasp from the Big Pilot. I don't recall a buckle from IWC to fit a 20mm strap- most of the straps taper to 18mm.

Bad news because:

Thx David, im sorry to hear that, my NATO nylon won't taper down to 18 mm :-(
Best regards: Robertus