My current ones are sched 80, but thread / thread. AA did not have any so he sent me to a plastics company in Commerce City - they had them (and I bought), but the hole size was just slightly more than the marine Depot ones I drilled for. Anyways, it looks like the Reefcentral gurus of beanAnimal design figured out the problem with the overflow and all of this is probably not really necessary. My weir was pushing bubbles down into the external overflow and causing the siphon issues...