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Old 07-23-08, 12:24 PM   #1
Triloc
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Torque wrenches 3/8 and 1/4 drive

Ive been looking at Torque wrenches and Im kind of puzzled.
When reading about it on the Park Tool website I come across this: The "TW-1 is 1/4" drive (includes 3/8 adaptor) and ranges from 0-60 inch pounds with compatible metric equivalents. "
What does 1/4 and 3/8 drive mean?
I tried to download the instructions but it said the document was damaged.
Any help?
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Old 07-23-08, 12:40 PM   #2
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What does 1/4 and 3/8 drive mean?
I tried to download the instructions but it said the document was damaged.
Any help?
It's a socket wrench. Sockets are interchangeable wrench or drive bit. A driver for sockets has a square driving member that the sockets fit on. They're available in a number of standard sizes, which measure the distance across the flats of the drive. 1/4 inch drive means that it's a quarter inch across the flats, and 1/4 inch sockets fit it. 3/8 drive means 3/8 of an inch across the flats, and takes 3/8 inch sockets.
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Old 07-23-08, 12:44 PM   #3
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They are just like wrenches for sockets etc. Some have a 1/4" square drive and others have a 3/8" square drive. Even larger torque wrenches for automotive use have 1/2" square drives. The torque measuring range increases with the size of the drive. The size standards for socket wrench drives are old English fractional inch measurements and were standardized many many years ago. There is no reason to change them to metric. Any standard units converter will give you the metric "equivalents".

To make matters more confusing there are 1/4" square and 1/4" hex drives...

Last edited by Torque1st; 07-23-08 at 12:57 PM.
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Old 07-23-08, 03:52 PM   #4
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Hmm ok so sockets. =)
Sorry about the stupid question but Im new at the mechanic stuff.
Does this mean that you need more than one torque wrench?
Or is one enough as long as you have several sockets?
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Old 07-23-08, 04:04 PM   #5
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Hmm ok so sockets. =)
Sorry about the stupid question but Im new at the mechanic stuff.
Does this mean that you need more than one torque wrench?
Or is one enough as long as you have several sockets?
The major thing you need to consider when buying a torque wrench is the range of torques that the wrench can apply. 0-60 in. lbs. will only be useful on the small bike fasteners (M5 and smaller: disc brake mounting screws, some stem screws, seatpost clamp screws). The next size up in torque wrenches (mine is a 25-250 in. lb.) will allow you to torque slightly larger fasteners plus all of the previously mentioned fasteners (25 in. lb. is a ridiculously low torque). This size of torque wrench will either be 1/4 or 3/8" drive. My next torque wrench is 10-100 ft. lb. and covers every other bike fastener that my other one doesn't (bottom brackets and crank arms). My larger torque wrenches (up to 250 ft. lb.) are only used for automotive fasteners.
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Old 07-23-08, 04:08 PM   #6
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Remember a torque wrench is most accurate in the middle portion of it's range. Try to avoid the extremes of the instrument's range when using it. Use a larger or smaller torque wrench instead.
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Old 07-23-08, 05:13 PM   #7
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I think a 1/4" drive torque wrench like the Park TW-1 is probably the best to have for bikes with carbon fiber and very light weight alloy components such as steer tubes, stems, handlebars, etc. I use a TW-1 for these applications and a 1/2" drive Sears beam wrench for bottom brackets and sometimes cassettes. I'm not saying these are the best but they're what I have. I think a 3/8" drive is too big for small light components. Torque is torque but the scale on a 1/4" drive TW allows for a more accurate measurement on light weight applications.

Al
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Old 07-24-08, 03:23 AM   #8
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I was actually thinking about the TW-2 for tightening the crankarms.
They need to be tightened to 12-15NM and the TW-2 spans from 0-67.8Nm (0-600 lb-in).
Would that do the trick?
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Old 07-24-08, 11:05 AM   #9
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I was actually thinking about the TW-2 for tightening the crankarms.
They need to be tightened to 12-15NM and the TW-2 spans from 0-67.8Nm (0-600 lb-in).
Would that do the trick?
The following assumes you want to torque correctly ...

If you take into consideration the usable range of the wrench and the accuracy of the wrench ... you may not be able to use that wrench to perform that torque.

First, this is a beam type torque wrench. Second, Park website never states accuracy of the tool so let's just assume +/- 2% of Indicated Value for. I could be better, could be worse, we don't know yet.

The industry standard for usable ranges of a torque wrench is 20% of full scale to 100% of full scale.
So if the top is 67.80Nm, 20% would be 13.56. So 13.56Nm would be the lowest acceptable reading with that torque wrench. The picture of the torque wrench at the Park site shows 5Nm increments. So to do your 12-15Nm torque, the pointer would need to land right on 15Nm.

And we haven't considered accuracy yet. Assuming a +/- 2% accuracy at 15Nm, this is a +/- .3Nm uncertainty. So a reading of 15Nm, could be anywhere between 14.7 and 15.3. Since 15.3 is outside the range of your torque (12-15) you would need to subtract that from the end of your torque, ie adjusted setting of 14.7. But wait, you can't torque to 14.7. The increments are 14nm or 15nm. Good torque practice with a dial or pointer indicator is to land on a "tick" mark ... not between "ticks"

So basically, in order to torque to this spec properly, you need a different torque wrench.

Yep ... those 0 to whatever torque wrenches sure look inviting but without knowing the usable range of the wrench or it's accuracy ... you might as well use your open end wrenches to perform the torque.
If you are going to measure your torque, measure accurately ... otherwise why bother.
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Old 07-24-08, 01:08 PM   #10
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Keep in mind that 60 inch pounds is only 5 foot pounds. Not enough to torque your cassette lockring (22 ft/lbs) or your crank bolts on a square taper (30 ft/lbs). I don't know the torque specs on carbon fiber bikes, so I don't know if that wrench is usable there. It sure won't help you on a steel or aluminum frame bike. bk
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Old 07-24-08, 09:17 PM   #11
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Just as a note, my CF steerer tube and handle bars both list a maximum torque of 45 in/lbs. It's a two bolt stem to steerer clamp and 4 bolt stem to handle bar clamp.
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