help with pin size for 1479

Those are usually short-end spring-bars. You can use regular springbars in a pinch, but the ends will pass all the way through the wall of the clasp, and potentially snag on fabric. You can buy them at a supply house, or your friendly neighborhood watchmaker might have an assortment.

So the correct Omega part number for the spring bar is 068st5307. I can't find any resources that state the length, only that it's 1.3mm thick. If I had to guess, it's probably 15mm or 16mm. As @Dan S stated, the ends of the spring bar may sometimes pass or not pass the wall of the clasp correctly, which could result in the entire watch slipping off your wrist if it fails. It's rare for aftermarket/generic spring bars to fit clasps correctly. If you have an Omega boutique nearby, just go and order the correct part. It's probably around $5.

To determine the length, you can just measure the internal dimension of the clasp. And just to be clear, I haven't had any trouble with generic clasp spring-bars. I was just suggesting that you buy short-end spring bars made for clasps, instead of the springbars used between lugs. In fact, I have an assortment that I purchased years ago, and have used them on many different clasps over the years. If you buy an assortment, you can probably get dozens for $20.

But since you only need one, I don't think $7 is outrageous. People selling these small parts put a lot of time into processing orders and shipping, and they need to make a profit.