These are countersunk thin sheet style rivet nuts which are ribbed to grip better against rotation with the dimensions as shown in the photo section of this listing:

• What you get: All measurements as shown in the  photo section of this listing are approximate to be used as a guide.
• 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 will be sent within the next business day of your payment. 
• Postage: All orders will be posted with Australia post.