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Can I use my wrench/spanner which has a box end / 12-point spline, and connect a breaker bar using a 12-point spline bit to it to get extra leverage.

Or is it more common to use extending bar/pipe over the wrench?

Is the first way possible, or would the line of torque be off-centre? Or would the spline bit / socket connection make this not practical?

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Extending any tool with pipes or other contrived schemes is to be discouraged. You are always better off to get a bigger tool for the job for the sake of safety and well being. –  Michael Karas Jan 28 '13 at 15:04
    
@MichaelKaras That sounds like something an engineer would say to a mechanic, as the mechanic smiles and rolls his eyes.... but seriously if money is not an issue it is always safer to not use makeshift tools. –  maple_shaft Jan 28 '13 at 15:26
    
After watching a friend slug a firewall from a slipped pipe, the eye rolling becomes much reduced when the mechanic is told to use the proper tools. Those welding seams are sharp, the process becomes bloody and slippery. Also, if you drop a 50 lb. gear in a truck transmission, don't try to save it from damage, it has enough force to cause the end of your finger to explode. (lessons learned from real life) –  Fiasco Labs Jan 28 '13 at 16:35
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2 Answers

The open end on a wrench is created to take only so much force before the jaws start to spread. If you need a Swede bar on the wrench, dispense with using the wrench.

Using a Swede bar on open end wrenches guarantees enough spread that they start rounding bolts after they've been permanently deformed. Wrenches are sized (jaw thickness and length) so the maximum torque using normal force will be about the range the bolt should be tightened to if you were to consult a bolt torque chart.

For similar reasons, you probably shouldn't be using Swede bars on box end wrenches.

For difficult to loosen nuts and bolts, you need a socket on the breaker bar and the socket directly on the bolt, preferably a 6 point socket so you don't round the hex.

Breaker bars are used because they're longer (more torque) and have no ratchet mechanism to break. You use them with a socket because the socket fully surrounds the nut and won't splay under the force (though I've split both 6 and 12 point sockets).

The 6 point socket usually is physically stronger than a 12 point and has larger engagement area (less likely to round the hex), though the newest technology is spline sockets which are designed to engage both nuts and bolts 1/3 the length of the flat back from the point and potentially are less likely to round off hex fasteners.

If you must use an extender (Swede bar), use it on the breaker bar as it is the most likely device you have that will take the excess torque. If the breaker bar breaks (I've done that as well) you need to graduate up a size on the drive (3/8" to 1/2") and try again. 3/8" drive stuff is for 5/8" and below, use 1/2" drive for 3/4" and above.

Consider using penetrating oil and mild heat if these fasteners are large and refusing to move. Also, how much rust buildup is there?

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+1 for no other reason than suggesting heat and penetrating oil before going through this hassle. Be careful how much heat you apply near penetrating oil though because it is flamable. –  maple_shaft Jan 28 '13 at 16:57
    
How in gods name did you manage to break a breaker bar? If I can't get it with a breaker bar I start preparting to destroy the bolt and replace it –  maple_shaft Jan 28 '13 at 17:02
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Friend's cheap imitation. For the record, I've never broken a Craftsman or Snap-on breaker bar. It pays to buy tools made with good alloy mix if you're planning on using them for more than light duty dilettante work. I've always loved Stahlwille chrome-vanadium for its light weight and exceptional strength. Also, having to work on farm tractors that have been around cows teaches you every means of fastener removal ever invented. No matter how much anti-corrosive you apply, cow crap always wins. –  Fiasco Labs Jan 28 '13 at 17:08
    
That sounds like BS to me ;-) –  maple_shaft Jan 28 '13 at 17:19
    
In the Dairy Industry, it's the lucky Bull who lives to be able to do so <grin>. –  Fiasco Labs Jan 28 '13 at 18:30
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If I understand correctly what you are describing then the spline bit in the end of the wrench would be connected to a standard ratchet or another wrench of some sort.

Torque by definition is a measure of Force x Distance considering a single Torque arm. The longer the distance the less force is needed to cause rotation over a fulcrum. When you place a pipe over the wrench or jimmy a bar in the wrench to give yourself more length, you are actually creating a second torque arm where the start of the second arm bears the full force against the end of the first arm. They are not contiquous so this force could cause a break at the weakest contact point of either arm.

In what you propose, the transfer of force at the weakest point between two arms will likely be the horizontal bit extending off the wrench, or in the case of using a gear action ratchet, the gear teeth or ball bearings.

With that being said, most geared ratchets probably have a maximum safe torque limit advertised somewhere on the package. A typical 1/2" ratchet would probably be in danger at just over 100ftlbs of torque. That isn't much and I am certain the teeth on a spline bit can take considerably more than this. I think it would be worth a try as long as you do not attempt this with a ratchet and you cannot find a pipe.

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I'm taking his word at it, a breaker bar doesn't have a ratchet mechanism, usually, the socket drive is hinged around a pin in the handle with a ball detent that lets you feel where 0, 45 and 90 degrees are in relation to the socket drive axis. –  Fiasco Labs Jan 28 '13 at 16:46
    
@FiascoLabs I thought it was worth saying because I have broken ratchets before by being stupid. –  maple_shaft Jan 28 '13 at 16:59
    
Yep, and it gets really painful if you are pushing the handle with your fist headed towards something solid. That "krrk-zick" sound they make during initial failure doesn't alert you quick enough to react. I was taught to only pull on them if more force than usual was necessary to start the bolt moving. Still got caught out once. –  Fiasco Labs Jan 28 '13 at 17:04
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