Hex fasteners, the ones most people call Allen head bolts, are on everything: machinery, vehicles, equipment, fixtures. The fastest way to ruin one is a hex bit that is almost the right size.

Hex head drivers sell steadily on our site. The 7/32 inch 1/2 inch drive hex bit socket and the 5/32 inch 3/8 inch drive version sit near the top of our order list, along with large metric hex bits like 10mm and 17mm. Here is how to pick them and how to keep from stripping the fastener.

SAE vs metric: close is not close enough

Hex sizes come in inch and metric, and some are very close to each other. That is the trap. A metric bit in an inch fastener, or the other way around, can feel like it fits. Then it rounds the socket the moment you put real torque on it.

If you do not know whether a fastener is metric or SAE, test fit both and use the one with the least play. In a shop that works on mixed equipment, keep inch and metric hex bits in separate, labeled rows. Stamped size markings, which our hex bit sockets have, make that easier to keep straight.

Impact-rated hex bit sockets

For impact use, you need a bit socket built for it. Two good examples:

These are one-piece style bit sockets built for impact duty. That matters because a hex bit takes a lot of twisting load right at the tip. A tool not rated for impact can twist or snap. If it snaps inside the fastener, you now have two problems.

Large hex bits: 10mm and 17mm

Some equipment uses big hex fasteners, and those need a big bit. We carry hex screwdriver bits like the 2150 10mm hex bit, with a 10mm hex shank and a 30mm overall length, and the 2357 17mm hex bit, with a 17mm hex shank and a 56mm (2.2 inch) overall length. Both are listed as High Speed Steel and heat treated.

These bits go into a holder or bit socket that takes that hex shank size. Before you order, confirm what your holder takes. A 17mm bit does you no good if the holder is built for something else.

Choosing the right length

Bit socket length trades reach for control:

  • Shorter (like 52mm): keeps the tool tight to the fastener. Less flex and wobble. Better in tight spaces.
  • Longer (like 60mm and up): gets past obstructions and into counterbored holes. But it puts more leverage on the tip if you are not straight.

If the fastener sits down in a counterbore, you need the length. If it is out in the open, go short. Most shops end up with both for the sizes they use every day.

How to avoid stripping hex fasteners

Most stripped hex fasteners are preventable:

  • Seat the bit fully. A bit that is only partly in puts all the load on the edges and rounds them.
  • Clean the fastener. Dirt, paint and rust in the hex keep the bit from seating.
  • Stay straight. Hex bits do not like angles. If you need an angle, use a different access tool.
  • Use the right size. Not the close one. The right one.
  • Retire worn bits. Rounded bit corners strip fasteners faster than anything.
  • Break a seized fastener loose by hand first. Then run it out with the impact.

If the fastener is already partly rounded, stop and think before you make it worse. Sometimes a fresh bit and a straight, firm push will do it. Sometimes it is time for an extractor. For more on failures under high torque, read our post on bit socket failures.

Where hex bit sockets show up the most

Here are the jobs our customers tell us they use these for most:

  • Machine and equipment guards, covers and housings, which often use socket head cap screws.
  • Brake caliper guide pins and suspension components on a lot of vehicles.
  • Conveyor, packaging and production line equipment in plants, where maintenance techs need the full SAE and metric spread.
  • Fixtures, jigs and tooling plates in machine shops.
  • Bicycle, motorcycle and small engine work, mostly in the smaller sizes.

A plant maintenance tech often needs a much wider size range than an automotive tech, and usually both inch and metric. If you supply industrial customers, plan your assortment around that.

Hand vs impact: which do you need?

An impact-rated bit socket can be used on a hand ratchet. A hand-rated bit should not go on an impact. So if you are buying one set for a field truck, impact-rated gives you more options.

Hand bit sockets still give better feel on light work, and there is nothing wrong with owning both. Our impact bit sockets category and hand bit sockets category list the full range of sizes.

Stocking hex bits for a shop or resale

For supply houses, hex bit sockets turn fast, but the size spread is wide. Look at what your customers work on. Equipment and industrial customers need larger sizes. Automotive customers go through the common small and medium sizes. If you are not sure where to start, our top movers are a reasonable guide: 7/32 inch on 1/2 inch drive and 5/32 inch on 3/8 inch drive.

If you buy for a fleet or a government agency, write the full spec: hex size, inch or metric, drive size, overall length, and impact or hand. That gets the order right the first time.

A quick check before every job

Before you put torque on a hex fastener, take five seconds. Look in the recess. Is it clean? Is the bit sharp at the corners? Does it go all the way in? Is there play when you rock it gently? If anything feels wrong, fix it first. Clean the recess, swap the bit, or try the other measuring system. Those five seconds are the cheapest insurance you have against a stripped fastener and an extractor job.

Warranty and value

Genius hex bit sockets and bits are covered by the Genius Tools Limited Lifetime Warranty against manufacturer defects. It covers defects, not normal wear. Bits wear when you use them hard, so keep spares.

The value is being able to stock the full size range without blowing the budget. Professional-grade CR-Mo bit sockets at a reasonable price mean you always have the right size instead of the close one.

FAQ

Can I use metric hex bits on SAE fasteners?

Only if the sizes are truly equivalent, which is rare. Use the matching system to avoid stripping.

Are the 466007 and 365205 impact rated?

Yes. Both are Chromium Molybdenum alloy steel, heat treated, with a black oxide finish, built for impact use.

What do the large hex bits fit into?

The 2150 has a 10mm hex shank and the 2357 has a 17mm hex shank. Use a holder or driver that accepts that shank.

Why do hex bits round out?

Usually the wrong size, a worn bit, partial engagement, or working at an angle.