Which screw drives to choose 1

[m.piron]

I have to choose between Hex (external) and Allen screw drives.

In my opinion, these are the pros/cons:

Hex, pros:
- less risk of strip
- possibility to use a pliers, if stripped
- possibility to put more torque in it
- thinner head

Hex, cons:
- aesthetically, not beautiful
- in a counterbore, need a bigger hole and a socket wrench

Allen, pros:
- exhist in cylindrical, rounded and countersunk head, aesthetically beautiful
- exhist folding hex key, just one tool for big variety of screws
- perfect to be used in counterbore holes

Allen, cons:
- it's easy to strip
- if stripped, hard to remove
- the socket may be filled with dirt
- if cylindrical head, the head is taller

My main goal is the simplicity, especially for maintenance.
About the allen screws, I love the aesthetic and the possibility to use folding hex key.
About the hex, I love it's reliability.

What is your opinion?

Thanks

 

[BrianPetersen]

All the factors that you mentioned and more mean that in a relatively complicated machine, you are going to have both, depending on the application.

Don't forget that Torx, e-socket, and XZN all have applications, too.

 

[BrianE22]

Allen heads have small diameters and will yield soft materials underneath them. Often times a thick steel washer is used with them.

 

[SnTMan]

Carriage bolts w/ square nuts

The problem with sloppy work is that the supply FAR EXCEEDS the demand

 

[btrueblood]

Allen heads are less likely to strip if you mandate that torque is to be applied with a square-ended driver, i.e. no ball-type ended drivers.

 

[DAVIDSTECKER]

You had better go look in your maintenance mans tool box before you make a decision.
Most contain the least amount of tools they can get by with.
Usually a Crescent wrench, two sizes of flat blade and one Phillips screw drivers, Channel Locks and what ever else fits into a 5 gallon bucket or a back pack.
I have found fold hex sets a pain in the back side compared to an "L" or "T" handle set.

 

[Stick.]

Whatever you pick, try to stick to just one if you can (and try to streamline the number of different sizes too) for ease of maintenance. DAVIDSTECKER makes a good point about keeping in mind what tools are available. If you are going to specify that any of these be torqued, make sure the sockets are available to fit the torque wrench (probably only a problem with allen heads). At an old job, one of my mechanics couldn't remove a gearbox from a machine because it was fastened with 12 point (external) drive screws and he only had 6 point sockets, so we had to wait for a different mechanic to come along with his tools. Whoever specified those 12 point screws probably wasn't thinking that someone might have a 6 point socket set instead of a 12 point set.

 

[Jboggs]

Top quality machine builders prefer socket heads. They generally perform better in most situations. But the point about maintenance tools is a very good one.

 

[m.piron]

You had better go look in your maintenance mans tool box before you make a decision. Most contain the least amount of tools they can get by with.

Good tips!
but, I don't know who, and with which tools, performs maintenance.
Thus I need to make the dismantling operations as simple as possible.

Whatever you pick, try to stick to just one if you can

Some screws are inserted in a counterbore, then need the allen head type. For this reason, I can use everywhere Allen screws, just to don't use two different type of head.
The only, big cons of that head type, is that in dirt environment the socket may be filled with dirt.

Top quality machine builders prefer socket heads. They generally perform better in most situations.

This is a good point of view, can you please explain better what did you mean?

 

[robyengIT]

we were used to fill immediately the Allen socket with soft "putty"

 

[Jboggs]

"Top quality machine builders prefer socket heads." Their experience over decades of design, use, abuse, and maintenance has shown that socket head screws are preferred. I have been designing special machines for 40 years. Socket head cap screws have become my default. I must have a good reason to use any other type, and only in specific applications. Most decent mechanics have ready access to a good set of allen wrenches, and if they don't I'm not sure I want them working on my machine.

The other advise you're being given here is to minimize the variations in sizes. I try to have no more than 2 to 3 different sizes of screws on any given machine, maybe 5/16-18 and 1/2-13 for example.

 

[EdStainless]

We used 12 point flanged head cap screws (Ferry).
They distribute load well, are easy to operate, and be removed if stripped, and look nice.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, Plymouth Tube

 

[TheTick]

If it's a choice between hex and Allen.., I choose Torx.

 

[m.piron]

"Top quality machine builders prefer socket heads." Their experience over decades of design, use, abuse, and maintenance has shown that socket head screws are preferred. I have been designing special machines for 40 years.

I'm curious, why?
It's about the reliability, easy of use, dimension...?

Thanks

 

[3DDave]

Maybe of interest:
Air Force Report on Fastener Recess Evaluation
a059171.pdf 118 pgs

http://www.dtic.mil/dtic/tr/fulltext/u2/a059171.pdf

(still available there)
suggested by

http://www.eng-tips.com/viewthread.cfm?qid=414407

 

[Jboggs]

"I'm curious, why?"
OK, just off the top of my head:
1. First, the only types of screws routinely used by machine designers are socket head cap screws (SHCS), Torx head, or hex head screws. Screwdriver type screws (like Phillips head) MIGHT be considered for something like holding a cover on, but that's all. No heavier duty applications.
2. Hex head screws require external wrench or socket clearance on all sides in all situations. SHCS do not, so they are easier to apply in many situations.
3. In my experience SHCS screws rarely ever strip the head (unless some doofus tries to use a 3/8" wrench in a 10 mm socket).
4. Ball end wrenches are not a recommended method and should be avoided, but they are at least an option with SHCS. No such option exists for hex head or Phillips head screws.
5. SHCS offer no external sharp edges (with wrench induced burrs) to rip clothing or skin.
6. Quickly engaging and using a wrench on a SHCS is usually easier and quicker than with a hex head head screw.
7. They are very commonly available in a wide range of strengths, materials, treatments, and sizes, in both metric and imperial standards.
8. SHCS look better and more professional, if that is a concern.

There are more reasons but I have to go.