23R312 up for sale is a lot of 10 self locking speciality nut used on the sea king H-3 helicopter , this nut appears to be blue anodized aluminum and has two small holes to mount of rivet this on the airframe the center has a self locking 1/4-28 thread in the center , these are in sealed bag with the tag on the front , nice new self locking fasteners for your project , see our store for more items like this , also see the photos for a picture of the public owned specifications related to these fasteners , thank you rwk