They are all for 1/4 inch rod or threaded rods, you have to drill it open to able to used a 3/8 rods.
Hi jk, prices of items are subject to many factors including a national average set by our corporate office along with collaboration from our manufacturers and vendors, where the merchandise is being sold, the type of materials and labor used to create the product, and other various, related aspects of online merchandising. the item is sold in pack of 20 but price states each. We appreciate your business and look forward to serving you in the future. Thank you for shopping Home Depot.