Primary or exploration line reel
Primary reels typically have up to 400 feet of line and are used for bridging the gap between open water and the main line in a cave. Primary reels can also be used to explore the interior of a wreck. Because wreck divers typically use #36 or #42 line, a primary reel holds much less line. The thicker line holds up better against sharper objects.
Exploration reels can hold 500 to over 1,500 feet of line and are used for exploring new cave or deep into the interior of a wreck. Exploration reels are much larger and heavier and can be more cumbersome. Avoid carrying large exploration reels unless they are needed.
Cost: $90 to $180
Safety or jump line reel
Safety or jump reels contain approximately 50 to 150 feet of line and are used for emergency purposes, such as repairing broken lines, searching for a dive buddy, or searching for the primary guideline or are used while performing jumps or gaps between lines, such as when cave diving. They are also used to deploy lift bags when open water decompressing. Whenever you enter an overhead environment, you should always carry an emergency reel. Safety or jump reels should be carried inside a pocket on your dry suit or clipped to a waist or butt D-ring. This allows for easy access.
Cost: $40 to $80
Safety or jump line spool
Safety or jump spools contain the same amount of line as reels but operate differently. Spools have been popular with cave divers for a while, but only recently been introduced to other overhead divers. The advantage of spools is their small size and easy, reliable operation. They are low profile, less cumbersome, and are jam-proof. Safety or jump spools should be carried inside a pocket on your dry suit or clipped to a waist or butt D-ring. This allows for easy access. They are also used to deploy lift bags when open water decompressing.
Cost: $20 to $40