i spoke w Holosun and they said the screw is 6-32 x 7.5mm, slightly shorter than 5/16 (this is the shorter proprietary screw with a narrow head). They’re in the process of making them available for order on their website. I was able to buy a bag of 50 for $17.50. They had to go with the narrower head to make room for the electronics in the newer versions of their sights. Holosun has excellent customer service, offering to send extra screws free, just need a pic of the sight’s serial no., but I needed a larger qty. I spoke with
kelviny@holosun.com through their customer service contact.