It's fixed - Goldtec track hub and EAI sprocket, 38 x 14. I've used these chains before and they can rust a little around the pins, but generally they hold up well. They're very strong and also don't start to wear for a long time, but once they develop any measurable stretch, they're finished within weeks. One might do 1000 miles' commuting compared to 500 miles for the KMC Z510 I've just taken off. Very crude in appearance.