Mklein and sons knife

The Loop at the bottom isnt to hold the blade in, its a lanyard bail. Common on fishermans knives. The knife itself is manufactured by Matthias Klein & Sons Tool company. Its called a Hawkbill. The Handle should be plastic, made to look like wood, the silver metal you are speaking of is either nickel, or regular steel. What you are calling copper is likely brass, as it is commonly used for knife liners. Hard to date, but they were around in the 80's. The knife style is also called an electricians knife, as electricians use them, however some people also use them for pruning knives which would explain why your fiance found it at a plant nursery. A knife from the 80's can hardly be considered antique, but can be valued as a collectable. The knives themselves were meant to be used as tools, like most other knives, and therefore probably werent highly priced. The company itself was founded around 1856 and it seems still manufactures tools today. They popularly catered to electricians, which explains the knife style. The knives in good condition go about 20 dollars. The knife would be best kept at home and used as a tool as its intended purpose, or give it to somebody working in the electrical business if you know one, perhaps even your fiance can use it to prune with.

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I have one.

Also the blade is likely not silver. if it is rusted and tarnished it is likely carbon steel, commonly used in most knives from the period. No tool maker in the right mind would use precious metals in a tool that would take so much abuse. Hope this was helpful