Electroplated, zinc plated, or zinc coated fasteners.

What is the correct term for a zinc electroplated bolt? Is electroplated sufficient, or is more proper to use “zinc plated”, or “zinc coated”? Or do all of these terms describe the same thing?

Also, how does this affect friction values when using plated bolts and nuts when compared to plain steel? Some sites I found say friction increases with coating, and therefore applied torque values will also need to increase for the same loading on a bolted joint, but other sites say friction decreases. But since each source uses different terms to describe the coating I am not sure if I am comparing the same things.

Here’s something about zinc plated vs zinc galvinized. I think zinc galvinized is what zinc coated would fall under. Electroplated doesn’t necessarily refer to zinc.

From here, it would be either zinc electroplated or hot-dipped to describe the two ways a bolt could be coated with zinc. Hot-dip is usually only on large fasteners as the coating is thicker than electroplate.

There are a few things bolts can be plated with (eg: cadmium or nickel) so specifying zinc is important.

No idea on the friction, or if it’s even significant. Most people just pull harder on the wrench if the bolt is hard to turn.

Total tightening torque is a function of nutface friction, thread friction, and thread extension. The lubricity of the finish will affect the first two, as will any lubricant that is used. As an example, cadmium has a lower coefficient of friction verses zinc, which means (all else being equal) a cadmium-plated bolt should be torque to a lower value verses a zinc-plated bolt.

I’ve never used it, but there’s a software program called BOLTCALC which does all the math for you. And MIL-HDBK-60 is a handbook that exhaustively covers the subject of bolt torque.

If it doesn’t say galvanised I would natural assume its zinc plated, sometimes you’ll see the term bright zinc or yellow zinc as well to describe plating.
Using the term coated is a bit confusing as zinc can be painted or hot sprayed, dipped or plated.