This package includes (8) Stainless Steel U-bolts and (16) Stainless Steel Flat Washers and (16) Stainless Steel Lock nuts. These U-Bolts are made in the USA out of high quality 304 Stainless Steel, and they along with the 304 stainless hardware included, hold up well in wet/salt water environments. The 3-1/16" width is the clear Inside measurement between the "Legs" of the U-Bolt. The 4- 5/16" Height is the inside dimension measurement from the top inside of the "U", to the bottom tip of the "Leg". ATTENTION: To determine the Height of the U-bolts You need, measure the total height of the metal and members to be "clamped" and add 13/16" for the nut and washers. To prevent "galling" (also known as "thread lock") use a hand ratchet or wrench to run up and tighten the nuts, do not use a an impact or powered socket driver. If a U-bolt is accidentally dropped in sand, thoroughly clean it and apply lithium grease to the threads to prevent galling. These U-Bolts will fit on 3" x 3" cross members, such as 3" x 3" box steel. Magnetism: In its originally formed state 304 stainless steel is Austenitic and not attracted to a magnet but when threads are machined into the 304 U-bolt rod and the bends are formed, those areas become slightly magnetic, but they are still corrosion proof. When a 304 u-bolt is placed on a smooth surface, a strong Neodymium magnet placed at the bend of the u-bolt is able to slide or move the u-bolt, but it won't be able to lift it up off of the surface (Grade 201 Stainless Steel u-bolts can be lifted up off of the surface with the same Neodymium magnet). Grade 304 Stainless steel is also referred to as "18/8" because it contains 18% Chromium and 8% Nickel which is twice the amount that is in it's less expensive, and less corrosion resistant cousin Grade 201. DAD-Tmw