Know Your Hub Standards

If you don’t know what hub standards you need for your bike you can’t get started.  Fret not, we’re going to hold your hand and explain everything.  We’re going to jump through the X major factors in determining what you need.  These include the following...

Terms and Definitions

  • Freehub/Driver
  • Dropout
  • Skewer vs. Thru Axle
  • Quick Release vs. Bolt-On
  • 6-Bolt vs. Center Lock
  • Boost
  • Rotor
  • Flange
  • Hub
  • Cassette
  • Plus


Open (Slotted) Drop-Out vs. Closed Drop-Out

This is an open (vertically slotted) drop-out and is associated with a skewer (QR).

This is a closed drop-out and is associated with thru axles.

Skewer vs. Thru Axle

A skewer goes through the hub's axle and secures the wheel onto the bike. The frame/fork will have a drop-out. Skewers can be quick release or bolt-on.

Thru Axles are a lot like skewers but they replace the axle. The frame/fork will have a hole for the axle, not a drop-out.

It is common for a skewer to be referred to as a Quick Release or QR for short. For example, "100QR refers to a 100mm wide hub that uses a skewer, the skewer could be bolt-on or quick release. If it is a thru axle it would have a "TA" in the description such as 110TA. In bicycle nomenclature "QR" refers to a skewer and "TA" refers to a thru axle.

As always there are some exceptions but we will focus on modern axle standards that are supported by Pub Wheels.

Quick Release vs. Bolt-On

Quick Release Thru Axle

Bolt-On Thru Axle

6-Bolt vs. Center Lock vs. Rim-Brake

6-Bolt is the official ISO (International Standards of Organization) system. It is just as it sounds, six bolts hold the rotor to the hub.

Center Lock was created by Shimano and is licensed to other manufacturers. It utilizes a spline interface and a lock ring to hold the rotor to the hub.

Hubs for rim-brake wheels do not have either of these features.

You can install an adapter onto a Center Lock hub to convert it so that is accepts a 6-Bolt rotor. It is not possible to convert a 6-Bolt hub to accept a Center Lock rotor.


Boost spacing was designed in order to make 29er wheels and frames stiffer. When rear hub spacing went from 142mm wide to 148mm wide, the front chainring had to also be moved out from the centerline by 3mm. The front hub spacing also changed from 100mm wide to 110mm wide. Boost spacing is what allowed plus tires to be installed on bikes because when the chainring is spaced out 3mm it allowed the chain to run in all gears without rubbing on the wider 3" Plus tires.

Freehub/Driver Standards

Driver vs Free Hub, HG MTB vs HG 11spd Road vs XD. There are three common types of freehubs/drivers. HG stands for Hyperglide. There are two common types of HG free hubs, MTB and 11spd Road. Shimano’s 11spd road cassettes are just a little bit wider than their mountain bike cassettes. XD drivers were created by Sram for their 1x systems because the XD driver allowed them to use a 10 tooth small cog whereas with the HG freehub the smallest possible cog was 11 tooth.

Points Of Confusion/Oddities To Be Aware Of

  • Easton freehub, EC90 SLX, EC90 SL, EC90 Aero, and EA90 SLX. Trust us, these are weird but thankfully also rare.
  • Rock Shox 4-Bolt Rotor mount. You don’t see these very often so don’t worry about it, unless you see it, then be very worried.
  • Fat Bike fork with 135mm Skewer (typical rear hub standard) and front hub spacing. 135QR was originally a rear hub standard until fat bikes came along and flipped everything upside down and sideways. Normally a 135QR hub had disc-brake-mount-spacing that was specific to the rear brake (different from the front spacing). Some fat bikes used 135QR hubs as front hubs because there wasn’t anything else available at the time. Some 135QR fat bike forks have front-brake-spacing and some have rear-brake-spacing.
  • Shimano 10spd Dura Ace freehub. Believe it or not there was a time not too long ago that Shimano was experimenting with new standards for their HG cassettes and freehubs. They wanted to make an aluminum freehub because it could be made lighter than their steel freehubs. What they did was made the peaks of the splines taller and left the valleys in the same spot. But they were only for certain, high end Shimano cassettes. This did not go over well with the consumers and Shimano pretended it never happened.
  • Sqraxle. Specialized once combined a skewer and an axle, they called it a Sqraxle. It was a through axle that fit into a drop out. Many years later someone re-invented it and it is now known as a Thru Axle.

How To Determine Your Bike’s Fit Factors In Regards to Wheels/Compatibility Requirements

Rear hubs generally have three fit factors

  1. Axle
  2. Brake/Mount
  3. Driver/Freehub

Front Hubs generally have two fit factors to consider

  1. Axle
  2. Brake/Mount

Measuring your frame to determine your axle size (Tools Needed)

  1. Tape Measurer
  2. Micrometer

Sometimes a frame/fork or hub will have the axle size written on it. Be aware that some hubs can be changed/converted from their original size with the use of converter end caps. For this reason we recommend always measuring the frame.

Step 1: Determine if your frame/fork uses a Thru Axle (TA) or Skewer (QR). This is done via visual reference. Skewers are almost always 5mm in diameter. Thru axles are commonly 12mm, 15mm and 20mm in diameter.

Thru Axle Hub (TA)

Skewer Hub (QR)

Step 2: Using a tape measure, measure inside width of frame/fork where hub contacts frame/fork.

Step 3: Visually identify if your drop-out in open (slotted) or closed. Measure the diameter of your frame/fork dropout/axle hole. Open drop-outs almost always use hubs with skewers (QR). The width of an open drop-out (QR) of a fork is about 9.5mm. The width of an open drop-out(QR) of a frame is about 10mm. *some exceptions apply

Step 4: Find the standard(s) in the following charts that matches your measurements.

Comprehensive List Of Hub Standards

135x5 QR 135x5 QR
170x5 QR 150x15 TA
177x12 TA Lefty Max
190x12 TA
190x5 QR
197x12 TA


135x5 QR 100 QR
141x5 QR (Boost) 100x12 TA
142x12 TA 100x15 TA
148x12 TA 100 Lefty
150x12 TA 110x15 TA
157x12 TA 110x20 TA
110 Predictive


120 BO, SS/Fixie/Track 9x1 BO
126 QR, Old 100 QR
130 QR, Road 100x12 TA
130 BO, SS/Fixie/Track
135 QR, Road
135x12 TA, Road


135 QR 100 QR
142x12 TA 100x15 TA
Older Post
Newer Post
Close (esc)

Email Sign Up

Sign up for helpful bike info and alerts on anything super special.

Age verification

By clicking enter you are verifying that you are old enough to consume alcohol.


Shopping Cart

Your cart is currently empty.
Shop now