What caused screws stripped?

Let’s assume that the material, hardness and size of the fastener spec all meet standards.  Given these condisions, why does fasteners damaged happen? 

Several reasons:

1.) Design of Screw

The difference among bolt head designs, such as cruciform or hexagon. Some design will make the screws stripped happen easier.  That’s because the contact between tool and bolt head is too narrow and the gap is existed, causing uneven force application and inefficient torque transformation.  You can check below table of screw designs.   

2.) Too Much Torque

Excessive torque will cause damage on screws. For example, while using the electric or pneumatic tools, the output torque is overloaded than what screws can bear.  Each screw and nut got the limited bearing torque.  We strongly recommend to use mechanical torque wrench to prevent excessive torque while screws stripped or thread damage (崩牙) will cause huge money loss or potential life threat. 

3.) Wrong Size

Each screw nut has its specific size.  You still can unfasten the screws with smaller size screwdriver. But you will find harder because of the poor torque performance and more damage on the screws. 

White area is hexagonal bit. Gray area is hexagonal nut.  The smaller bits will cause larger gap between screw and bits.  The torque is concentrated on single point too much.

The downsides of common screw designs listed follows:

1.) Hex or 6-Point

The hexagon socket and hexagon bits driver are designed for “point contacts”, which relatively easily cause the tool and the nut holes wearing.  That is so called “stripped screws”. 

In addition, the driving Angle is 60 degrees, which torque transmission is poor.  (Theoretically, 0 degree is the optimal torque transmission angle. )

It will make screw stripped very easily if the torque is concentrated on single point.

2.) Phillips, or Pozi 

This type of screw is easily to cam-out when loosened or locked. Because the contact area of tool driver and nut is not fully seated.  It is easy to get slip from the bolt.  The user may subconsciously push too much power downward when locking the tool to avoid cam-out, which may damage the screw driver bit. The screw is not fully seated due to the contact face, and that's why the screw stripped happend sometime.

The bevels cause some of the rotation to twist upward.  That’s what we call “Cam-Out”.

3.) Torx

Torx's torque transmission is 15 degrees, more efficiency than Hexagon.  In other words, the user can save effort while rotating.  But there are still power concentration problems and the possibility of stripping cannot be completely avoided.  In addition, just like the hexagon screw, the vertical face could prevent the driver from stripping (cam-out).

The power concentration is downward naturally to avoid the fitting incomplete problem. The vertical face could prevent the driver from stripping (cam-out).

The following is a quick comparison of common nuts in the market.

To sum up, it is recommended to use star screw nut if a screw needs to be removed regularly and the cost of stripping is very high.  Sometimes the cost of butter fingers will drive you or your boss crazy.

If change the screw nuts are no longer option, chose the right tool will be more important.  The stripped screw cause not only time loss and money, but maybe the entire mechine can't worked at right time. 

Tien-I manufactures porfessional hand tools, such as hand socket bits, power socket bits and impact socket bits, from 1/4"DR to 1" DR, regular Phillips, Pozi and Star, Slot, 5 Point, Ribe, Triple Squre...etc.  

Since 2003, Tien-I has supplied the professional hand, electric and impact bit sockets to top hand tool brands worldwide. Check with our sales-team to see what we can do for you.