As Quoted on the Contents list of the ETS PSP:
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Scalpel Blade - back-up to your usual pocket or sheath knife. First aid. Use wood stick(s) as handle, wedge in end or between two and secure with wire or duct tape.
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In a previous job I used scalpel blades, usually just in my fingers. We got out of date unused scalpels from the local hospital. They are sharp enough to do delicate work with little pressure and still hold them in your fingers. For larger work I've put them into an art knife handle. They were a smaller size than the one in Doug's PSP.
Never needed to use one in a survival situation though. They would be easier to make a handle for than a razor bade.