What kinds of fences are there in show jumping, and how big can they be?

• Vertical: "an obstacle that requires an effort in height", with its parts in one vertical plane.
• Spread: built so that "it requires an effort both in spread and in height". Oxers and triple bars are spreads.
• Height: never more than 1.70 metres, or 1.65 indoors, except in the special high-jump competitions.
• Spread: not more than 2 metres, or 2.20 for a triple bar.
• Made to fall: obstacles must be able to be knocked down, "while not being so light that they fall at the slightest touch or so heavy that they may cause Horses to Fall".
• Cups: poles rest on supports 18 to 20 millimetres deep and must be able to roll.
• Safety cups: approved release cups hold the back pole of every spread.
• Combination: two or more obstacles between 7 and 12 metres apart, needing successive efforts.
• Numbering: a combination has one number, with letters for its elements, such as 8A, 8B and 8C.
• Jumping it: each element separately and in order, with no circling between them.
• After a stop: all the elements must be jumped again.
• Faults: counted separately at each element and added together.
• Flags: one red and one white at a vertical, and at least two of each at a spread.

The glossary has the obstacle, the combination, the related distance, the knock-down and the refusal.

The limits on size keep the sport within what a horse can do safely, and the safety cups on the back pole of a spread exist because a horse that lands on a fixed rail can somersault. Combinations test whether a horse can adjust its stride between fences, which is the real difficulty of a big course.