Galvanized Nut With a Plain Bolt? Why OEMs Needs to Match Fasteners Or Else
OEMS ask many questions about ideal fastener choices, ordering processes and the use of specific fasteners. One common question from OEMs involves a mash-up of galvanized nuts and plain finish bolts. Can that combination be done successfully?
There are several reasons why OEMs do NOT want to mix hot-dipped galvanized nuts with a plain finish bolt. In fact, this combination puts your joint at risk.
Specifications of a Hot-Dipped Galvanized Nut
During the galvanization process an additional 0.002" to 0.006" (or between 2 and 6 mils) of zinc ends up on the bolt threads. Because of this inevitable alteration, hot-dipped galvanized nuts are tapped with an oversized shape to ensure proper thread engagement. Attempting to use this tapped oversize nut with a plain bolt will result in slippage and a loose fit.
On the Other Side of the Coin
Some OEMs wonder if they can use plain nuts on galvanized bolts. Your fastener distributor will offer the same emphatic answer as above--no. The opposite problem occurs when using a plain nut on a hot-dipped galvanized bolt. Because the plain nut has not been tapped to accommodate for the additional layer of zinc on the bolt threads, you'll end up with an overly tight fit.
While this may seem like a good problem, easily solved with a powerful tool and a heavy hand, the reality of assembling this combination is another story. The nut will strip and gall those bolt threads, making the entire joint a waste.
Chasing the Threads
Avoid chasing the threads of a galvanized bolt in order to make it fit with a plain finish not. Chasing involves re-cutting the threads after the galvanization process, and removes the layer of zinc necessary to maintain corrosion resistance. The plain nut may fit, but your bolt will quickly deteriorate without the protection of that zinc coating.
OEMs should always pair a plain finish bolt with a plain finish not, and use hot-dipped galvanized nuts with galvanized bolts. Your fastener distributor will confirm that cutting corners by mixing and matching will only result in a weak joint and fastener failure, putting your entire application at risk.
