These are the open end large-flange style 304 stainless steel rivet nuts and they are ribbed to grip better against rotation with the dimensions as shown in the photo section of this listing:

• What you get: All measurements are approximate and to be used as a guide only.
• Quality: All products are of the high quality and meet the relevant international standards.
• Stock: We carry a large inventory of stock so all orders can be sent within next business day of your payment.
• Postage:  Your order will be posted with Australia Post.