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How To Avoid Breaking Spanner Bits

Avoid Breaking Spanner Bits

Broken Spanner Bit

The spanner drive style is still an uncommon drive style for most people to just have lying around.

This uncommon bit makes screws more resistant to tampering and removal without the proper bit. Due to this, a spanner bit is often referred to as a “tamper-proof” or “security” bit.

The Problem With Spanner Bits

As great as spanner “snake eye” bits are for adding security to an assembly, they also have some downfalls. Spanner bits are made to fit a very specific drive size. If they are used with the wrong size it becomes increasingly likely that the bit will break.

Spanner bits are also more prone to snapping than any other bit type. The spanner bit has two prongs that are inserted into two holes in the head of the screw. Pressure is then directly applied to only those two prongs (across a very small area) which causes the screw to turn. Other bits can have as many as six sides pushing on the head making it less likely that they will break by spreading the load across multiple points of contact.

Spanner bits are commonly avoided for this reason but there are actually a few easy steps you can take to avoid most of the common reasons spanners break.



Steps To Avoid Breaking Spanner Bits

Always Pre-Drill Into Hardwood

Hardwood can be particularly difficult for screws to cut into. We recommend pre-drilling a pilot hole even when the screw has a self-drilling tip. Pre-drilling a hole removes much of the wood that would be in the way and allows a screw to more easily install.

Avoid Coming To A Hard Stop

Drilling into knots or using a screw that is too long where it can hit metal on the back of the installation surface can cause the screw to seize in place. This sudden seizure will place all of the pressure upon the bit prongs and more than likely cause them to snap.

Avoid Over-Installation (Over-Torquing) Of The Screw

When installing the screw, make sure to stop once the head reaches the installation material. Attempting to screw the fastener in further will increase the amount of torque required to turn the screw dramatically.


Watch As Bob demonstrates this with one of our own spanner bits.

*No spanner bit regardless of quality will stay in tact if you do not take care when installing spanner drive screws. It’s the nature of the bit design.

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