Sizing (complex)

Sizing is a very important when it comes to the fit of a bit. Sizing affects the functionality of both the mouthpiece and the cheekpiece.

When placing a Bombers bit in the horses mouth, the Bombers engraving and size stamp should be on the left side of the horses face, facing outwards. Bombers came up with this innovative idea to only add stamps and sizing on the left-hand side of the bit to ensure all of our bits will be correctly used without confusion. By just looking at the size stamp (and on some bits, the Bombers sticker) you will be able to determine which way the bit should go in the horses mouth – preventing using the bits backwards or upside down.

If the sizing of the bit is incorrect it can affect the functionality of the mouthpiece as pressures will not be distributed accordingly and can cause a cheekpiece to add or remove too much pressure that it will not be effective as per its design.

Here are some examples of how sizing can affect mouthpiece functionality:

Single or Double break – When the bit is too large, the center joint(s) can create pressure points on the wrong points of the mouth. When a bit is too large it can move through the mouth. There have been some cases in which joints have applied pressure across the bars – instead of the center of the tongue (which it is designed to do)

Ported – When a bit is too large it can create enough space to allow the mouthpiece to rock and create increasing pressures on the bars and possibly tongue pressure through the rocking movement.

Here is an examples of how sizing can affect cheekpiece functionality:

When a bit is too large, it can allow the mouthpiece to have too much mobility in the mouth. A fixed cheekpiece is designed to limit mouthpiece movement and create stability. When the mouthpiece moves too much in the mouth, it can create increasing bar pressure and squeeze on the bars, as well as having the potential to cause friction which could lead to the creation of sores.

Sizing - with Bomber and Claire

Sizing can be determined through a number of methods:

Method 1:
Using a Bombers Bit Measure.

Method 2:
Using a wooden stick and martingale rubber stoppers on either side.

  • Place martingale stoppers on either side of the wooden stick and leave +- 20cm between the stoppers.
    Place the wooden spoon in the horses mouth and ensure there is a stopper on either side of the horses face.
  • The wooden spoon should be placed in the mouth, similar to how a bit would sit in the mouth.
  • When the wooden spoon is set comfortably in the horses mouth, slide the martingale stoppers to sit snug against the horses lips. (without pushing lips in)
  • Without disrupting the placement of stoppers, remove the wooden stick from the horses mouth.
  • Set the wooden stick down on a table and use a tape measure to measure in between the stoppers and note down the measurement.
  • The measurement noted is equivalent to “X” in the bit measurement graph (which is equivalent to a fixed cheek- solid mouthpiece combination)

Method 3:
Using a correct fitting mouthpiece-cheekpiece combination to derive the size of the horses mouth, and then using the bit measurement graph to determine the correct size of the “new” bit combination.

Eg. Your current bit is a Loose Ring (loose) Elliptical (double break) size 140mm and you want to buy a Drop Cheek (fixed) Happy Tongue (solid), but you are unsure of size.

According to the Bit Measurement Graph, it will mean that: x + 15 = 140, therefore “X” = 125mm.

According to the graph, the Drop Cheek Happy Tongue is a fixed cheekpiece – solid mouthpiece combination and is equal to “X”, therefore the new mouthpiece-cheekpiece combination’s correct size is 125mm.


  • A solid mouthpiece fits the same as the mouth size
  • A semi-broken needs an additional 5mm to set, as it has some movement
  • Flexible and broken mouth pieces need an additional 10mm to set as they relax down in the horses mouth


  • Any mouthpiece paired with a fixed cheekpiece does not need to add additional millimetres to the size as a fixed cheek piece is meant to sit snug.
  • Any mouthpiece that is paired with a loose type of cheekpiece needs an additional 5mm added, this 5mm is to prevent any pinching of the lips. However, when checking fit no more than 2.5mm should show between the lips and hole the cheekpiece goes through.

Bombers uses millimetres to have a wider range of bit sizes.

When the millimetres are converted into inches, it does not always give a whole number, hence our table converter is only there to offer a reference point to ensure sizing up or sizing down will be done accurately.

Bombers (mm)
































Assessing the fit of the bit can be done by assessing the external fit of the cheekpiece.


A Fixed type cheekpiece is a cheekpiece that is directly attached to the mouthpiece.

A Fixed cheekpiece is meant to sit snug against the face, this prevents the mouthpiece from being pulled through the mouth. A Fixed cheekpiece allows for a quicker application of pressure than a loose ring and a slower release of pressure.

Here are images of a correct fitting Fixed cheekpiece:


A Loose type cheekpiece is a cheekpiece that is not fixed to the mouthpiece, the cheekpiece moves through a hole in the mouthpiece, allowing the mouthpiece to be able to slide on the cheekpiece.

A Loose cheekpiece does require an extra 1.5mm on either side of the cheekpiece to create space for the loose ring to rotate, preventing pinching of the lips. A Loose cheekpiece is Bombers preferred cheekpiece. A Loose cheekpiece allows for a quick release of pressure, returning the mouthpiece to neutral in the mouth, it allows for a slow application of pressure.

Here are images of a correct fitting Loose cheekpiece: