I bought this as a replacement part for my Iron Cobra Junior double pedal. I had been using only the right pedal with a single beater, and the original spring assembly had got lost.
Fitting is very straightforward - there is a collar that slides over a mounting post on the upright part of the pedal, and the threaded bolt then slides through that. The bolt has one side planed off to fit through the semi-circular hole - this prevents it from rotating once installed.
Similarly, the bottom nut has a triangular inner flange which fits into a triangular hole on the collar - again this prevents it from rotating or vibrating loose once set to the desired tension.
Note that this package does not include the actual spring itself - this is just the assembly to hold the spring at the bottom. I still had my original spring, but be aware that you will need to buy one separately if you don't have yours.
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