The on-line and searchable portion of Sweden's patent database only goes back to the 1970s, so I cannot find a patent for the coupling link G.
The coupling link G was a significant product, so my guess is that Gunnebo did file and gain a patent.
The names 'hammerlock' 'hammerlok' all relate to the force needed to seat and unseat the clevis pin. The clevis pin can be removed and replaced, but limits are placed on how many times a pin can be hammered out before it ought be replaced. Gunnebo of course sells replacement clevis pins.
Gunnebo has an office in downtown Stockholm. I have a vague memory that it has a small museum display about the history
of the company dating back to the smithy in the village of Gunnebo in the 18th century.
And learn the lesson: if you're innovating, come up with a name that ties the product to you. Gunnebo could have marketed their coupler as a 'Gunlink', 'Gunnelink', 'G-link', 'G-coupler', 'G-spot' or whatever ...