What is a shaft bow?

Shaft bows are only used in Russia, Finland, the eastern Baltic countries and, perhaps oddly, Sicily. It is used in single horse or troika (three horses in a row) harness - in the latter case it's put over the middle horse.

It acts as a spring and allows for a smoother start with faster horses. They're often painted. If you want a culture to do unusual harness - this is one possibility.

Shaft bows are generally wooden - metal ones have been tried, but tend to crack in the cold climates this harness is popular in.

Painted shaft bow on the middle horse of a troika. Image source: Wikimedia commons.

What are terrets?

Terrets are the little metal hoops on the collar and saddle of driving harness that the reins/lines run through. They're designed to prevent the lines from dropping too low and possibly tripping the horse. There are also sometimes terrets on the rear bridles of a large team.

Here the reins have been tucked through the saddle terrets to keep them out of the way.

What are horse brasses?

Horse brasses were used to decorate the harness on driving horses, especially in nineteenth-century England. They date back, as far as we know, to the pre-Roman period, but reached their height under the Victorians. (Although called brasses, the older ones were made of bronze or even silver).

Victorian horse brasses showed all kinds of designs including crosses, animals, horse shoes, hearts, and of course family crests.

In fact, during the Victorian era, the number of heavy brasses seen on working horse harnesses were so high that animal welfare movements campaigned for a reduction, which resulted in the production of lighter brasses which were stamped rather than cast.

Horse brasses are still commonly collected today, but less seldom seen on horses simply due to the decline in working horses. This image of Shire horses plowing (It's actually a fake shot) shows horse brasses "in the wild" on the strap behind the saddle.

Image source: Malcolm Morley via Wikimedia commons.

What is a bearing rein?

Remember Black Beauty and the issue surrounding bearing reins. A bearing rein is sometimes called an overcheck or checkrein.

The purpose of the bearing rein or overcheck rein on harness horses was to elevate a carriage horse's head - and at the time they were often used in a manner that was uncomfortable for the horse and made it hard for them to lower their head enough to pull properly. Bearing reins in that form disappeared...because of the novel (These days, we think of Black Beauty as a cool kids' book, but it was written to highlight the abusive practices and fashions of the time).

Overcheck reins are still used on some harness horses, but are fitted much more loosely. They're most often seen on Hackneys and other horses with naturally high head carriages. Some believe they help prevent the reins from being caught in the shafts (but if they're holding the horse's head that high, they're probably too tight.

The other context in which you might hear "overcheck" is with animals that are used to carry small children or disabled riders. A loose overcheck rein is often fitted to these horses with the primary purpose being to stop the animal from putting its head down to eat - which with a light or insecure rider can result in the rider being pulled over the head by the reins (don't laugh. I've seen it happen). In this case, the overcheck or bearing rein is fitted very loosely and not intended to interfere in any way with how the horse holds its head.

In this picture of a show Hackney, the bearing rein is the strip of leather that appears to be running along the top of the neck. Source: John Goetzinger via Wikimedia Commons.

What Does Harness Look Like?

This one's for the illustrators. I've seen some very inaccurate depictions of horses in harness, so I'm going to pull up some visual aids here and talk about it.

There are several kinds of horse harness. One of the big differences is whether a collar is used or not - collars provide a more effective pull, but are heavy on horses that might be asked to go fast.

Image source: Amanda Slater via Wikimedia Commons.

So, let's start with this. These are plow horses, although they are wearing "show" harness - probably for a plowing contest. The weight of the plow is settled on the collars around the horse's neck. The horse collar is a very efficient and comfortable (for the horse) way to have an equine pull weight. The stiff framework supporting the collar is called the "hames". The plow itself is attached to chains which are connected to the sides of the collar. Chains are used because their weight helps them fall into place better than straps or ropes. The chains run through a strap around the horse's body, which in harness terms is the "saddle". A strap along the back supports britching, and there's also a strap between the horse's legs. All of this is to keep the saddle and collar from slipping. The decorated brass discs are called "horse brasses" and are an old British tradition. The blinkers help keep the horses from spooking and being distracted.

Image source: Rooh23 via Wikimedia Commons.

This is a horse pulling a cart in collar harness - you can see the same collar and a similar bridle, but this particular harness has no saddle. Instead, it has two straps over the back which support the shafts, which are then also secured to the collar. Again, the weight of the cart rests primarily on the collar. The rest is all to stop stuff moving and, in this case, to prevent the shafts from moving up and down.

Image source: Adam Jones via Wikimedia Commons.

A rather more typical horse-drawn carriage - note the short chains between the end of the shaft and the collar (which is also a much lighter collar). This harness does have the more typical collar. As this is a double, the single shaft runs between the horses - this is typical.

This is "breast" or "breast collar" harness - the weight of the cart is supported on a strap across the horse's chest. This kind of harness weighs less than a collar and is easier to put on, but isn't efficient or comfortable for heavy weight. In this picture, note the lack of breeching - instead, there's a crupper which runs under the horse's tail. Also note that both this team and the one above appear to be wearing bonnets - those are to keep the flies out of the horses' ears.

Either of these would be correct for a typical horse-drawn carriage pulled by a pair of horses.

Image source: Vickusin, via Wikimedia Commons.

This shows a four-in-hand in modern competition. Here, the shafts are on the outside of the back pair of horses, called the "wheel" pair. There are no shafts next to the front or "lead" pair. Note the strap holding the lead pair together - this is to keep them straight and at the correct distance from each other without shafts in the equation. The driver here also has two sets of reins or "lines" - one for each pair of horses. This allows him to turn the front pair separately from the rear pair when making tight turns. This sort of setup would be correct for a stage coach or large carriage with four (or more) horses.

Image source: Marjon Kruik via Wikimedia Commons.

A slightly different setup, also correct. The shaft is between the wheel pair and the horses are rigged out with breast collars rather than neck collars.

Image source: Benny Mazur via Wikimedia Commons.

When four horses isn't enough. A six-up of draft horses pulling a wagon - this would be a correct setup for large scale farm deliveries. The shaft runs between the second and third pairs of horses. (The middle pair is called the swing pair). Hitches of eight or even ten horses are known. Just add horsepower...

Image source: Quistnix via Wikimedia Commons.

This is a more unusual setup - a tandem of ponies. It also shows very classic britching very well on the first pony.

And another less common arrangement - a four abreast of Norwegian Fjords. Image source: Pete Markham via Wikimedia Commons.

Image source: Jon via Wikimedia Commons.

Today we design cars with a barrier between the chauffeur and the inhabitants so they can talk freely. This is how they used to do it. This arrangement is called "postilion" and the driver, instead of being in the carriage, is riding one of the horses. The downside - you needed one rider for each pair of horses, and postilion was mostly abandoned - but is still occasionally used, as seen here, by the British royal family. But if your characters don't want the coachman to overhear them...

Image source: Jorge Royan via Wikimedia Commons.

This is racing harness and is quite different! The shafts are secured to the saddle and the "collar" is a single strap around the horse's neck with a strap between its legs. There are two sets of shafts. (Again, note the ear bonnet). The cart being pulled here is called a "bicycle sulky" and weighs no more than 40 pounds, so there's no need for heavy straps on the harness. This kind of harness is only seen in modern harness racing.

And last one, I promise:

This is actually a training setup. The saddle and britches are present and the lines are tucked through the saddle, but there's no collar. This setup is used for "ground driving" a horse - which is done as part of training before putting a driving horse to a cart and also used by some people to train riding horses.