Question on Bolts

[Phil Waterman]

Hi Stuart

You didn't say which vehicle you are working on but from the metric size I'm going to assume that it is a vehicle that uses metric bolts. Only mention this as it is a pain to do repair work which is a mix of metric and inch fractional.

Now to your question on 'My question is what is the advantage and disadvantage of the finish such as Plain, Yellow Zinc and Zinc in these locations?"

The biggest problem I found with most modern bolts is getting the paint to stick to them if you are painting them. Plain bolts with no protective coating other than the oil base coating need to be cleaned to get a good bond with paint.

Yellow Zinc and Zinc paint does not bond well to at all with out etching the bolts. The metal etch that you use to prep bare steel before painting will etch or out right remove the Zinc coating. The paint will stick better but the bolts and hardware will rust if not well painted.

On things like bumper bolts I stand the bolts in a shallow tray of the metal prep so just the heads are etched. Leaving the threads still coated.

My experience is that the plain zinc and shinny zinc is generally used on standard grade bolts while the yellow zinc is usually used on grade 8 bolts. Not being impressed with much of the standard grade bolts hardware, coming out of China too many broken bolts and stripped threads. Deffinitly not the same quality of bolts CMPs were built with 60+ years ago. I have gone over to using all grade 8 bolts and hardware. Buying most of it in bag lots of 25 to 100 from Fastenal http://www.fastenal.com/web/home they sell in quantity but if you are going to hardware store or auto parts to buy 10 or 15 regular grade you can probably by 25 or 50 grade 8 for nearly the same cost.

Fastenal of course has all the metric and inch dimensional bolts from their web site it looks like there are quite a few outlets in Canada.

Cheers Phil

[rob love]

Aside from the painting problem, the finish resists corrosion and seizing. While those plain finish bolts may look OK, you won't be so happy in a couple years when you have to cut or break them all off.

Grade 8.8 metric is the equivalent of our SAE grade 5 bolts. As to putting grade 8 (or 10.9 metric) on everything, that is fine 95% of the time, but there are applications where you prefer the bolts to bend slightly than to shear, so you should use the correct grade of bolt. Frame applications come to mind....in many spots the lower grade is the correct bolt to use.

The DIN 933 merely is the standard (vs DIN 931) of whether the bolt is only threaded on the lower portion or if it is threaded all the way up to the head. DIN 931 is partially threaded, DIN 933 is fully threaded. Mind you, on short bolts, both specs result in the same product.

If you really want to get confused, I have seen bolts with both the metric rating and the SAE markings (lines on the head). When you see those, you may need to get out the pitch gauge and the calipers to figure out what they are.

I used to manage some pretty good nut and bolt selections when I ran various tool cribs over the years. The non-mechanic users often displayed problems understanding the metric/vs standard, the grading systems, and even the fine/course factor. The best bet in the end was to put a cage around the whole works and only the mechanics got a key. Not only did it reduce the number of metric bolts stuck into standard holes, but it also sure cut down the wastage and pilfering, much to the dismay of many of the combat arms fellows.

[Lynn Eades]

Just to add a finer point to a part of Robs post.
Metric bolt tensile strengths are identified by "Class", where as American thread form bolts are by "Grade"
So a metric Class 8.8 is roughly equivalent to an imperial Grade 5 bolt. (using Robs example)
Rob, hybrid bolts go back to Canadian Carriers in WWII.Ford of Canada built carriers with BSF bolts with heads and nuts to fit American spanner sizes.
Now days the plating on a lot of fasteners tends to be for show. A lot of zinc washed bolts will be showing rust after sitting in a bit of water on top of a 44 gallon drum, for a day or so.
Some high grade fasteners like FX brand bolts (grade 10.5) have a gold color type finish on them that might be marginally better.
During WWII Cadmium plating was a finish commonly used. Dodge used the stuff on their bolts. 75 years later with the heads half rusted off them, those bolts , once cracked off, will undo with your fingers. Those bolts are the nicest I've come across in 40 years as a mechanic. Cadmium is a toxic heavy metal. It's not used anymore.
Be aware that torque figures are lower for plated bolts compared to black bolts.
Also, be advised not to use high grade bolts in a heat situation.

[rob love]

While I admittedly don't have the corrosion problems of the East (Ont/Qebec etc) , I have had success using the silver loctite antisieze on nuts and bolts. It is of extremely high temp rating, and as you will find when you atart using it, it transfers from the bolt to your fingers, your fingers to everything you touch for the next hours, then back to your fingers when you touch them again.

We used to use them on the tapered shock pins for the M113. These were a bugger to get off normally.....sometimes you just removed the shock mount and left it with the shock. Other times, on the non-removable pins, you cut the shock bearing off the pin. But with the pin pre-coated lightly with the antiseize, the shocks came off very nicely.

We also used it as a lubricant in the HLVW remote shifter cup, so it is good for more than just antisieze.

As to the blue or red loctites, those will be dependant on the application, and really does not have anything to do with corrosion protection.

Lynn: There is a short filmstrip about carrier maintenance form the war. In it, they warn that the bolts for the firing rest angle iron over the radiator are 3/8 NF, and not to mix them with the various BSF nuts and bolts on the rest of the carrier. I also agree with your like for the Dodge bolts. I have worked on numerous M37s, and the hardware on them is unsurpassed in quality by anything else.

Perhaps a good example of the cross SAE/DIN would be the hotchkiss jeeps, where the threads were SAE on the engine, but with metric heads. (At least that is what I was told by a guy who had one...I have never had one myself.)

[Bob Carriere]

For non critical parts, like sheet metal on a cab 11.....

Try TSC....Tractor Supply C...... you can buy by the pound any size of washers and bolts all zinc and grade 5..... at about $3.75 a pound.... just grab a handfull of these, those, them and that and go to the cash...... saves having to count and put them in individual bags.

I have yet to buy a pound of 1/4 - 20 nuts and count them to see if it is cheaper than Fastenal..... but faster and cheaper than Home Despot...... last batch was $46 for 12.82 pounds........

Flea markets who sell prebagged fasteners can be a bargain but you must be able to read the head symbols and carry a caliper...... some sell High Quality manufacturing surplus.....

Bob C.