Have printed the hollow handle capsule for my Cold Steel Bushman knife. It's basically a thin walled cone with a lip on each end for snap caps. But I had to print several test cones first to get to the exact angle of the handle's inside shape for a truly snug fit. The right length is also important, as at the blade's side opening the handle is squashed somewhat, which starts crushing the capsule if you force it in too far. Still, the inner volume of the capsule is slightly more than 4 inches in length. It sits inside the handle very tightly, so I cannot just shake it out. To remove it you need to press with your finger from the blade side, and it will pop out. But I plan to melt a little piece of plastic into the small side hole in the handle to fix it there semi-permanently. Also I may decide to make it completely waterproof, it's easy to seal both caps with the nail polish over the inner lip. Just as an example I put inside a magnesium stick with small ferro on the side, large plain ferro rod, and a small diamond sharpener. There is plenty more space left inside for maybe some fishing stuff and tinder, at any rate I plan to stuff it tight to prevent any rattling.

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