
Mostly tin foil but they seem to work. If it's a critical application I'd spend the extra money on better quality fuses, but as long as they work well, are the right amperage, and fit well.

β‘ 20 Amp Single Circuit Breaker for Q120
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π Bussmann GMA 5A Acting Cartridge Listed: Reliable and Efficient Cartridge Fuse for Your Automotive Needs
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