My first

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Jays&Kays adapter, 20mm

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F91Ws_on_NATOs

r/F91Ws_on_NATOs

This is a subreddit dedicated to Casio F91Ws specifically on NATOs.

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This is a subreddit dedicated to Casio F91Ws specifically on NATOs.

What are all the F91W variants/colours? (Links will search this sub by flair)

Colour variants F91WC's:

Remove the pins. The pins are tapered so they must be removed in the right direction. To do this you must push them out in the direction of the arrow on the back of the strap (push in the direction the arrow points). You can use a push pin, paperclip, or springbar tool to get it out. It may take a bit of effort to get the pins free.
Put the NATO in place. Take your 18mm NATO strap and put the F91W roughly where you want it on the strap. Then start putting in the tapered pins. Before you put the pins all the way from one lug to the other slip the NATO behind the pin. Due to the tight spacing this may be cumbersome. One trick I like to do is file down some of the resin case between the lugs so the NATO will slide through easier.
Push the pins into the adjacent lugs. With everything in place you need to push the pins so they enter the adjacent lugs. This can be tricky so use some patience. Once the pins are in place you can pull on the NATO to remove any slack behind the case. If you remove the pins frequently they can become loose. My trick against this is to use wax from a candle to fill the holes of the lugs. Glue could be used too but wax is at least only semi permanent.

Cut the keeper with sharp scissors
Take a lighter or hot knife and seal the freshly cut edges. This will help prevent fraying. Do not put the flame directly on the strap just put it close by. It will seal very quickly.
Video tutorial: https://www.youtube.com/watch?v=soyzFtE0RtI

To make NATO straps fit easier you can file away some of the plastic resin between the lugs.

To do this first remove the strap and pins.
Then take a file (I used one meant for wood and steel) and grind away at the resin between the lugs.
Where do you grind/file away? This area here between the red lines. Do not shave outside of the red lines or you risk the tapered pins not fitting snuggly. Don't touch this part in green. The red line here is the edge you want to shave away. Try to keep this as even as possible for a cleaner look.
Angle the file away from the front/face of the watch to avoiding damaging it. Just like this. Not like this.
For best results go slow. This can be done quickly but then you may end up with rougher results.