A B.I. hexagonal nut means it’s coated with black iron instead of galvanized iron. The latter has zinc to prevent corrosion. The disadvantage of this, however, is it can’t be used in gas lines as the zinc starts to react with gas, causing flaking, overtime. So using B.I hex nut in such applications is better.

From the name itself, a hexagonal nut is a nut with a hexagon-shaped head. Threads of the hex nut are either right-hand or left-hand. The size of hex nuts refers to the nominal thread diameter, which is typically from ¼” to 2 ½”. 

Hex nuts are used with other fasteners such as bolts, threaded rods, anchors, studs, or screws. Other fasteners may also be used along with it.

Using hex nuts with other fasteners need careful installment to ensure full thread engagement. When using with bolts or screws, make sure that either of these two is long enough that there’s two more full threads beyond the nut face once it’s tightened.

The primary difference between the ordinary and imported hex nut is the materials used. Both are of high-quality, but the latter is more reliable for heavy applications.