Rigging Glossary: .	Arbor: A carriage which holds the metal weights used to balance a lineset in a counterweight system. Each lineset has its own arbor. Counterweight: One or more sandbags (in hemp systems) or metal weights (in counterweight systems) that are use to balance a lineset in order to make it easier to move. Head Block: An overhead pulley which changes the direction of lift and operating lines between the loft blocks and the sandbags (in hemp systems), an arbor (in counterweight systems), or winch (in automated systems). Lift Line: The rope or cable running from the load to the sandbags, counterweight arbor, or winch, depending on the type of fly system. Lineset: One or more lift lines working as a unit to lift, lower, or suspend a load. Loft Block: An overhead pulley which supports and changes the direction of a lift line cable between the load and the head block.
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There are three major types of fly systems. Bill Sapsis, of Sapsis Rigging, Incorporated explains them:
Hemp Systems:	Sandbags Good morning. There are three basic forms of rigging systems being used. The oldest and least common is what is typically referred to as a hemp system. The name is no longer accurate as we no longer use hemp or any other organic material in rope. Polyester is the fiber of choice for almost all of our rope rigging needs. We still use the name, "hemp," because stagehands tend to be more traditional by nature and a "synthetic system" sounds silly. The hemp system uses rope for the lift lines to the pipe batten. The counterweight most often used in a hemp system is sand. The sand is kept in different size bags so you can change the amount of counterweight being used without having to actually remove sand from a bag. In a hemp system, the operator pulls on the lift lines in order to fly the lineset out. Flying the lineset in depends on gravity, so it's necessary to keep the hemp set slightly batten-heavy (heavier on the load side than on the sandbag side) to make sure you can lower the batten when you want. Belaying pin and trim clamp The basic operation of a hemp system starts with lowering the batten to the stage deck and attaching the lights or scenery to it. The lift lines run from the batten up to the grid, through their respective loftblocks, over to the headblock and down to the fly gallery or stage floor where, when the batten is not being moved, they are tied off to a belaying pin. The sand bags are attached to the lift lines at the grid by means of a trim clamp or, more commonly these days, a cable Sunday. The Sunday is a loop of wire rope that is choked around the lift lines. Once you have roughly the same amount of weight hanging on the lift lines as there is weight hanging from the batten, you can then raise and lower the batten with relative ease. When moving the batten there are two things you have to watch out for in a hemp system: Getting hit in the head with a sand bag as you fly the batten out, and Landing a sandbag on the pin rail and puncturing the bag with one of the pins.
Counterweight Systems:	In the late teens or early twenties, a new form of counterweight system became popular. This system involved using cast iron or steel bricks as weights in place of the sand. The bricks took up less room than the sand bags because they were much more dense than sand, and the bricks were cleaner. No more sand dropping down onto the stage floor and into the performer's hair. While the principle was pretty much the same as the hemp system, the equipment and the operation were different. The rope lift lines were replaced by steel cables. As with the hemp system, the cables went up through their respective loftblocks and over to a headblock. However, when they came down from the grid they did not hang loose but were attached to the top of a weight carriage. This carriage is where the technician placed the cast or steel bricks to balance the system. So, when the batten was brought to the stage floor the weight carriage went up to the grid. Whatever was placed on the batten was balanced with weight placed in the carriage. Then it was a simple matter of pulling the rope to raise or lower the batten. This system is the one most prevalent today but is losing ground to automated systems.
Automated Systems:	The third and final system, the one gaining in popularity, is the automated system. Basically, an automated system is a machine that removes the need for counterweight (sand or bricks) and also the technician to pull the rope. A winch, which is an electro-mechanical assembly of a motor, gearbox and cable take up drum now does all the work. The technician simply pushes a button that tells the winch what to do. In most cases the lift lines, which are steel cable, go up through their respective loft blocks just like the other counterweight systems. But instead of a headblock the lines are wrapped around a steel drum. When the drum turns in one direction, the lift lines wrap on the drum raising the batten. When the drum turns in the other direction, the lift lines play off the drum and the batten lowers. An electric motor and gear reduction unit (gearbox) are what turn the drum. There is no need for counterweight or an operating rope. An electrical control system sends instruction to the motor telling it which way to turn the drum and how fast it should move the batten. The gearbox then takes the information from the motor and converts that information into the required strength and speed needed to carry out the operation. The upside to a automated system is that you can now move large and heavy elements much more quickly, accurately, and efficiently than a technician could by hand. The down side is that automated systems do not have a brain and cannot always adjust quickly enough when there is a problem in the system. Automated systems are significantly more expensive; typically, an automated system will cost approximately 3-4 times what a manual system would cost.