<p>Torsion strain exceeding screw strength. It's likely that 3" of wood is creating some friction, even though your pilot hole is nominally larger in diameter. You might try a 3/16"ø pilot hole and see if that reduces the amount of torque needed. Deep holes of narrow diameters in soft materials are never perfectly straight so the extra room of a wider pilot hole is a fast and cheap solution. I remember being warned early in my career to pay attention to the screw head type and do not expect the same results when you use a screw gun on a screwhead designed to be turned by hand (as traditional panhead and button head slotted screwheads are). You might also trying lubricating the screws to reduce the torsion load. Beeswax being typical and safe here for both wood and metals. You could expect that even though some heads didn't snap off, that they may do so in service - being under the same stress. You can also use a higher strength screw preferably with a head designed to be power driven.</p>

CC BY-SA 3.0
2018-02-17T15:38:55.583Z
2018-02-17T23:37:47.480Z
2018-02-17T23:37:47.480Z
herb guy
<p>you can use thicker screws and/or coated screws .. here in the EU we have <a href="http://spax.us/" rel="nofollow noreferrer">SPAX</a> .. heh, tough as nails they are! The screws with Torx heads are good as you can drive them hard .. if you use a hammer drill to drive them in you have the advantage of the tapping effect. last point .. If you have access to Robertson head screws .. the ones with the square socket .. you can drive them as hard as a Torx head and they tend to be cheaper</p>

<p>have a look at <a href="https://www.diffen.com/difference/Hammer_Drill_vs_Impact_Driver" rel="nofollow noreferrer">this comparison</a> of power drivers</p>

CC BY-SA 3.0
2018-02-23T21:51:54.687Z
2018-02-23T21:51:54.687Z
vulcan_
<p>I've been converting a school bus for several months, and I've driven thousands of 3/4" sheet metal screws with no issue. However, when I try to drive longer screws (3") through a couple inches of wood and into 14ga steel on the other side, their heads invariably snap off barely after seating in the metal.</p>

<p>I'm using #12x3" sheet metal screws with 5/32" pilot holes. What could the problem be?</p>

CC BY-SA 3.0
2018-02-19T11:57:11.337Z
FYI, this kind of question is also relevant on https://diy.stackexchange.com/ - you might find it useful if you have any further questions.
walrus
<metalworking>
Why are longer sheet metal screws snapping on installation?
threewordphrase
# Why are longer sheet metal screws snapping on installation?

(Asked by: username_0 on 2018-02-17)

I've been converting a school bus for several months, and I've driven thousands of 3/4" sheet metal screws with no issue. However, when I try to drive longer screws (3") through a couple inches of wood and into 14ga steel on the other side, their heads invariably snap off barely after seating in the metal.

I'm using #12x3" sheet metal screws with 5/32" pilot holes. What could the problem be?

**Tags:** metalworking

> **Comments:**
> **username_1**: FYI, this kind of question is also relevant on https://diy.stackexchange.com/ - you might find it useful if you have any further questions.  

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## 2 answers

### Answer by username_2 on 2018-02-17. Score: 5 | Accepted answer

Torsion strain exceeding screw strength. It's likely that 3" of wood is creating some friction, even though your pilot hole is nominally larger in diameter. You might try a 3/16"ø pilot hole and see if that reduces the amount of torque needed. Deep holes of narrow diameters in soft materials are never perfectly straight so the extra room of a wider pilot hole is a fast and cheap solution. I remember being warned early in my career to pay attention to the screw head type and do not expect the same results when you use a screw gun on a screwhead designed to be turned by hand (as traditional panhead and button head slotted screwheads are). You might also trying lubricating the screws to reduce the torsion load. Beeswax being typical and safe here for both wood and metals. You could expect that even though some heads didn't snap off, that they may do so in service - being under the same stress. You can also use a higher strength screw preferably with a head designed to be power driven.


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### Answer by username_3 on 2018-02-23. Score: 0

you can use thicker screws and/or coated screws .. here in the EU we have [SPAX](http://spax.us/) .. heh, tough as nails they are! The screws with Torx heads are good as you can drive them hard .. if you use a hammer drill to drive them in you have the advantage of the tapping effect. last point .. If you have access to Robertson head screws .. the ones with the square socket .. you can drive them as hard as a Torx head and they tend to be cheaper

have a look at [this comparison](https://www.diffen.com/difference/Hammer_Drill_vs_Impact_Driver) of power drivers


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