Is it advisable to use an impact wrench on small fasteners, for removal only. When say a 13 mm bolt will not budge will the impact wrench just break it off? I've always used just a regular ratchet but I'm thinking using a regular ratchet may be worse for breaking a stuck fasten since it just twists it. Whereas an impact wrench strikes it will lots of little hammer type strokes to remove it. Which method is best? Of course some penatrating oil would be used in either instance.

first you're going to get many different answers on this. you need just remember 1 thing. there are 1/2 impact guns, 3/8 impact guns, air rachets with torques up to 100ft lbs. and there are butterfly guns. you need to match the gun to the job. and when there are adjusters on the gun always start with the lowest setting for torque and work up.

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I think impact wrenches in general are less likely to snap a fastener.
The lever arm on a manual socket wrench generates a lot of lateral shear force. Plus the percussive force is more likely to shock it free.

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My air ratchet doesn't provide any more torque than would hand tightening with a manual ratchet...and I believe that is deliberate. So you should be fine either loosening or tightening.

An impact gun is a whole different story...

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We use hand held, hand hammer impact tools all the time on aircraft nuts/bolts/screws. Same on motorcycles...
These just impact once for each hit, so it gives control to the tool ..

the use of impact will help loosen a bolt that doesn't want to budge. Obviously you can snap a 13mm bolt with a 3/8 ths drive. But you risk breaking the bolt using impact. Can you heat the bolt? What about access to any exposed threads? If the bolt passes through its connecting member the threads on the back side can be cleaned and lubed proir to removal. Alternately, gently feeling for the bolt loosening then re-torquing, following that sequence to loosen. Otherwise, snap it, grind it drill it and heli-coil it. Easy-outs work for bolts that are "easy to get out" and that is all.

Just my 2 drachmas worth.

good luck and may the winds of patience blow in your favor...

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Thank to all for your responses.

This question came from my experience trying to remove bolts holding a catalytic converter to an exhaust manifold on a Mercedes. I was having quite a time getting them loosened. I did eventually get them off after applying penetrating oil an letting them sit for 2 days. I just used a regular ratchet as I was concerned I might break the bolt with an impact wrench or twist it off with a 3/8" air ratchet.

My ½" drive Snap On impact is the IM 6500 HP which has a lot of adjustability as far as power goes; like 5 setting in the low power mode and 5 in the high power mode.

It sounds like I could have tried the impact at very low power setting to see if it would break the bolt loose. I think I'll try the impact in the future with small fasteners, although starting on a low power setting. Incidently when I said 13mm bolt I meant the bolt head was 13mm not the actual bolt.