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Metal Work Primer

We, Suzuki hobbyist, come from a variety of backgrounds and skill levels.  As you navigate through Zooki-land, you may be presented with information or specifications that are foreign, especially when it comes to metal.  Whether it is steel or aluminum accessories or tube bumpers   things like material type and thickness, sizes and diameters can be confusing.  Id like to help clarify a few things for you.

First, lets go back to elementary school for some book learning.

Remember back in Mrs. Wilsons fourth grade class and she was trying to teach you fractions and decimal equivalents and you thought heck, Im never going to need to use this when I grow up.  Well this isnt a bad place to start.  It would be good to memorize a few decimal equivalents or at least get a chart that converts fractions to decimals.

If you were really paying attention to Mrs. Wilson then you know that a fraction is really a division problem. To convert a fraction to a decimal you divide the numerator by the denominator (the top number by the bottom number). Dust off the calculator and as an example to convert a fraction     lets say, to a decimal, press the 1 key, then the divide key, then the 4 key, then the equals key wow it comes up as .25.  So the decimal equivalent of   is .25.

To help you on your way lets get a feel for whats going on.

A 64th of an inch is about .015 (spoken as 15 thousandths, actual .0156).

A 32nd of an inch (the little lines at the beginning of most tape measures) is about     .030 (spoken as 30 thousandths, actual .0312).

A 16th of an inch (the next little lines on the tape measure) is about .060 (actual .063),

And an 8th of an inch is .125 (spoken as a hundred twenty-five thousandths).

Thinking in thousandths of an inch comes in handy when considering new pistons for the motor.  Oversize pistons are offered in .020, .030 or .040 thousandths of an inch larger than stock.  The machine shop will rebore the cylinders by one of those dimensions and the oversize pistons will fit nicely. 

So during next years campfire bull session at ZookiMelt and somebody is describing an engine rebuild and says thirty over pistons youll know exactly what theyre talking about.   See how much Mrs. Wilson was trying to teach you!

Before we trigger too many memories of elementary school, lets dive into the metals business.  Sheet metal is classified by thickness in a gage (or gauge) format.  Below is a chart that shows a few of the popular sizes and their decimal equivalents.













































These are just a few there are gages from 1 to 38 and more.  But if you went to the local steel warehouse these would be common sizes.  Youll notice the greater the number the thinner the material.  For example, 24gage (.023) is thinner than 16gage (.059).  There is a little bit of difference in thickness between mild steel, stainless and galvanized sheets.  And to get things really mixed up, there is a difference between ferrous (steel, magnetic) and nonferrous (nonmagnetic, i.e. aluminum, brass, copper, some stainless) sheet metal gages and on top of that there is a difference between sheet gages and wire gages.  It can be a tad confusing thats why a gage chart is handy.

After 7gage, typically the sizes switch to fractions 3/16ths, , 3/8ths, and so on.  The thicker sizes no longer are defined as sheet but are known as plate.  Dont be a rube and ask for a piece of sheet metal it would be plate.


There is hot rolled steel (H.R.S.) and cold rolled steel (C.R.S.).  Each description identifies what state the metal was in when it was processed.  The metal was either hot or cold when it was rolled to its final dimension.  Generally, hot roll is a little softer and has a mill scale surface.  Kind of a rough, dull texture and the scale does flake off as the material is formed.  Cold roll has a nice smooth, bright surface, is a little harder, and usually has a film of protective oil.   There is also another product in sheets know as HRP&O meaning hot roll, pickled and oiled.   The surfaced has been modified, pickled to remove the scale and oiled.  This gives the look of cold roll at a less expensive price.  Bar stock is also available in both hot roll and cold finished with hot roll being cheaper.  Plate and structural shapes including angles, channels, and I beams are hot rolled.

I forgot to mention that there are mill tolerances for all the dimensions of a piece of material, so the chart lists the theoretical thickness the steel producer shoots for.  For example a sheet labeled 16 gage (.059) may actually measure somewhere between .0568 and .0635.  Typically the steel mills produce the sheets on the thin side of the tolerance.  Dont freak out if the supplier sells you a piece of 16 gage and it measures .057 instead of .059.


Galvanized is the basic mild steel sheet processed with a coating of molten zinc applied on both sides.  The sheet starts out the right gage and the extra thickness is the coating.  The zinc coating makes the material more corrosion resistant but more difficult to weld and to paint.  As you weld, the zinc is burned or melted away so the base material can be welded.  Unfortunately, with no zinc the corrosion resistance is out the window.  Youll have to touch up the welds with some cold galvanized spray paint. 

Other similar items in the galvanized line are: Galva Neal a galvanized sheet that accepts paint better and gal alum an aluminum coated sheet used where heat and corrosion resistance is needed (i.e. automotive exhaust systems).


Stainless comes in a wide variety of alloys.  The common types are a 300 series and a 400 series.  300 series is known as nonmagnetic and the 400 series is magnetic.  If there is a question of what type it is, the magnet test works well.  The 300 series is very corrosion resistant and common alloys would be described as a 303 or 304 stainless.  The common stainless alloys in the 400 series are 416, 420, are less corrosion resistant and in some applications will actually rust.  The 400 series stainless are used in fasteners and are also used in automotive exhaust systems.  Rounds, flats and structural shapes are available in stainless as well as sheets. 


When it comes to measuring aluminum it goes back to decimals and not gages.  Aluminum sheets are described in thousandths of an inch and not gages.  Typical sizes are .032, .040, .050, .063, .080, .090, .100, .125, .190 for example, you would characterize .125 aluminum as one twenty-five or eighth inch aluminum, instead of 11 gage (.120).

You could probably write a masters thesis about aluminum alloys.  There are alloy numbers and heat or temper numbers and hardness ratings.  Heres the tip of the iceberg.  Most sheets would be 3003 or 5052.  Both are easy to fabricate, bend and weld.    6061 is sometimes described as aircraft aluminum.  6061 is harder and more difficult to fabricate but is very strong hence the aircraft moniker.  Angles, tubes and structural shapes are typically extruded and are available in a couple of alloys with 6061 being the most common.

The whole gage system is a weird system that was figured out a long time ago so we arent going to change it now.  Its best just to pick up a catalog from the local steel supplier and refer to the gage charts, product listings and begin to learn something Mrs. Wilson would be proud.

Practical Application

Here are a few things to remember:

1.      16 gage (.059) is about a sixteenth of an inch (.063) thick.

2.      11 gage (.120) is a little less than an eighth of an inch (.125) thick.

3.      10 gage (.135) is a little bit bigger than an eighth of an inch (.125).

4.       7 gage (.179) is about three sixteenths of an inch (.188) thick. 

Repairing some body panels would require perhaps some 26 gage (.018) or 24 gage (.023) easy to bend and form by hand.  The front fender off my zuk measures about .035 or 20 gage.  A gas tank or a flat panel that needs some strength makes 16 gage (.059) or 14 gage (.075) a better choice although some equipment might be needed to bend these heavier gages.  I checked the deformed stock front bumper off my zuk and it measured about .065. 

.100 or .125 aluminum would make a nice gas tank or storage box.  The tread plate door panels might be made of .063 or .090 thick aluminum.  Speaking of tread plate, both in steel and aluminum the thickness is the base material and the little bumps are taller.

Pipe and Tube

There have been more than a few discussions about pipe and tube when it comes to building support structures for your truck.  Let me first describe how things are measured. 

Pipe is a tube that transfers liquids and gases.  It is listed as a nominal (read approximate) inside diameter.  The wall thickness is commonly known as a schedule as in schedule 40 or schedule 80.  Below is a chart showing the common sizes of pipe and their dimensions.



Wall thickness

Sch. 40


Wall thickness

Sch. 80
























Again, we are faced with a system that was originated many years ago and seemingly has no rhyme or reason.  It took me a long time to figure out there is no dimension on a piece of inch schedule 40 water pipe that measures of an inch.  You have to bump up to schedule 80 wall thickness before you find any dimension close to what they call the pipe. 

You might ponder why there is no inch dimension to the young lad in the Lowes plumbing department next time youre doing a project around the house.  That might be worth a chuckle.  

Tube on the other hand is a little easier to understand.  Tube is described as an outside diameter (O.D.) and a wall thickness.  For example a 1   x 11 gage tube is actually (within mill tolerances) 1 inch outside diameter and it was made from 11 gage(.120) thick steel.  In my steel catalog, 1 tube is available in wall thickness ranging from 20 gage to .5.  Now that is a piece of tube 1 O.D. with .5 wall makes for a .5 I.D. wow!  Tubing is made from a strip of flat steel that is processed through a tube mill.  From a coil the strip steel is roll-formed into a round shape and welded along the seam (imagine a tube mill that can roll a strip of thick steel into an 1 diameter tube!). 

DOM tubing is then drawn over a mandrel that gives it a more uniform shape and size and reduces any protrusion from the welded seam on the inside.  DOM is an additional step in the process, is a better quality tube, so it costs a little more money.

All tube is first made round and then is processed into square or rectangle shapes.  The same description applies a 1 square tube x 16 gage would measure 1 x 1 outside with a wall thickness of .059.  A 2 x 5 x 7 gage rectangle tube would measure outside 2 x 5 with a wall thickness of .179. 

Hopefully things are starting to make sense with tube, the O.D. remains constant and the wall thickness changes.  The thicker the wall the smaller the inside diameter or dimension.  If the inside dimension is what you want, referring to the gage chart makes calculating the inside dimension easy.  O.D. minus 2 X the material thickness = the inside dimension (You know what size tube do I need for the cheater on my hi-lift handle).

Now back to the discussion between pipe and tube.  Remember, pipe is a tube that transfers liquid or gas and should not be used in the construction of any roll cage that is going to protect human beings.  Even when thinking that moving up to schedule 80 pipe would be ok.  The only benefit I see in pipe other than supplying the needed ingredient for the gas logs in the fireplace, is the ability of a 1 pipe to telescope into a 1 pipe.  This comes in handy in making an adjustable height welding table or a T-stand for the table saw.  It might work as an axle/pivot for the swinging spare tire rack on your Zuk.  But it should never never be relied upon as a protective structural material.

Tubing with adequate wall thickness is the desirable material for roll cage and armor applications.  You cant go down to the muffler shop and get them to bend up some exhaust tubing for a rear cage.  The stuff is too thin.  Just ask them what the gage is and then refer to the gage chart.  It will scare you and youll realize why you have to put a new tail pipe on every other year.

You may hear some tube chassis and racecar parts made from chrome moly tubing.  This is just another alloy of mild steel that has you guessed it chrome and molybdenum added to it.  It improves the tensile strength of the steel from about 50,000 psi to 85,000 psi. 

Those numbers may or may not mean anything to you but it gives you the idea that chrome moly is stronger and thats why the NASCAR boys like it when theyre upside down trying not to mow the grass in the infield with their helmet visor.

Armed with the knowledge of metals, gages, wall thickness, and dimensions, it should help you make bettter decisions when reviewing products for the Zuk, especially in the comparison of products from different manufacturers.  A well-designed tube bumper made from 11 gage will be substantially better than the stock bumper (.065).  If one manufacturer boasts of a product made of 16 gage and another manufacturer has a similar product made of 11 gage that might explain a price difference between the two and bring into the thought process questions of durability.  It might help you determine if a product is designed as a showpiece or something that is really functional.

All in all, steel is a good thing.  Thank heavens somebody figured out how to take a little iron ore, throw it in a blast furnace, add a few chemicals and voila give us something to bend, weld and fabricate into a world-class trail buggy.

I hope this information will be beneficial as you make plans in building your perfect off-road Suzuki.


07/24/10 08:19:51

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