Compatibility means that you can for instance attach shafts of one shaft manufacturer to dart barrels made by a different company.
Steel tip and Soft tip
"Classic"steel darts have solid attached tips. This means they can't be used for soft tip darts. A classic steel tip dart has the fixed tip on one end and a thread for the flight on the other.
Soft tip dart barrels have threads on both ends. One is for the plastic tip and one for the shaft. You can use these darts for steel if you replace the plastic tips with replacement tips for steel darts. Such replacement tips are available in various shapes.
However, there are steel tip darts that also have two threads. They are usually meant for use with "movable tips". Such tips will reduce bounce-outs. These dart barrels, although intended for steel only, can also be used for soft tip. Just replace the movable tips with soft tips. On the other side, most soft tip darts can be equipped with such movable steel tips. Only "most" because some movable tip systems require a thread deeper than usual. For instance Unicorn's Hammer Head system can be used on normal soft tip darts, while Harrows' Power Point system can't.
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