In the late 1970s, when I owned Bertram GmbR in Solingen, Germany, we produced a "knife-opener" made of nickel silver. In essence it was a pocketknife liner that was polished and trademarked, with one end dubbed off so that it would fit into a nail mark.
If you have ever broken a nail trying to open a strong springed knife or a difficult soda-pop can, then you know how helpful the proper tool for such a purpose can be. As I get older, I find that my once stout nails are becoming more and more like my hair, thin and fragile. Slipjoint knives, unless perfectly engineered and perfectly made, have become very difficult for me to open without an assist. Square tanged knives are very difficult without the proper tool.
Always a believer in never using a crow-bar or pry-bar when a simple jimmy would do, I have designed a very simple tool. It measures only 1-7/8" long and 5/8" wide and it is a mere 0.038" thick. The curved front edge has been machined to a precise bevel for a secure fit into the nail mark on any antique or modern slip-joint knife. I have added a positioning button for the thumb. On the basic tool it is black Rucarta™. We also offer the tool at slightly higher prices with Cocobolo and with stabilized Wooly Mammoth Ivory. This is the tiniest of tools and is made of spring tempered stainless steel. It should last for many years of hard use.
A.G. Russell™ Steel Thumbnail Black Rucarta
A.G. Russell™ Steel Thumbnail Mammoth Ivory
A.G. Russell™ Steel Thumbnail Cocobolo
A.G. Russell™ Steel Thumbnail Black Rucarta - When ordered alone
A.G. Russell™ Steel Thumbnail Cocobolo - When ordered alone