There have been a few questions regarding the not-yet-released S scale coupler over the last few days. I'll try to answer those as best I can here.
1. When will it be available? Probably late January. No promises though. It has to be right first.
2. Metal or Plastic? Metal. The 3D printing process provides plastic that I investment cast to turn it into metal. The metal is a zinc aluminum alloy not far from what the die cast couplers are made of.
3. Assembly Fixture? No fixture will be available. Are you kidding? These things are HUGE.
4. How many in a pack? Don't know yet. I haven't thought much about it. I haven't thought much about the price either. I'll have to sharpen my pencil there because 3D printing cost is based on volume and as some one pointed out these are 2 1/2 times bigger than the HO couplers by volume.
5. Will they work for On30? I guess. On30 typically uses KD #5 couplers or clones which means the mounting arrangement will be different for the Sergent couplers. The KD S scale coupler actually uses a mounting pin that is smaller in diameter than the HO scale #5 coupler. The Sergent coupler will use the smaller pin. The S Scale coupler will also be a type E coupler which I would guess was not too common on 30" gauge lines. It certainly wasn't common on 36" gauge lines. Still, it would be exactly 3/4 size in O scale. I guess that's a reasonable compromise. Personally, I don't like compromise, but that's just me.