Manual labor has always produced great overall strength, but nothing compares to the forearms of blacksmiths. Hammering and lifting pieces of steel all day long makes those forearms really powerful and that gripping strength deadly. One thing we have to look at and learn from when it comes to strength training of the arms is the variety of grips and angles to work with, repeatedly.
The first one is pretty obvious, hitting with the hammer works the brachialis, biceps and all the triceps heads works antagonistically. At all moments, the wrists flexors and extensors are keeping balance and the flexor and extensor carpi ulnaris are trying to hold down the beating, protecting the wrist.
Then, there is the crushing grip of the hot burning heavy steel they hold with a heavy ass clamp. While they must hold the clamp tightly to prevent the steel from moving, with the other arm they beat the steel to mold it in the way they want, hit after hit, millimeters at a time.
You should view your triceps/biceps/forearms training the same way. In fact, you can only be as strong as the weight you can handle right?
Include pronated, supinated and neutral grip, fat grip bench press and pull-ups, pinch grips curls, ulnar flexion and extension with a broomstick. You could as well fill up a bucket with sand and work finger extensions and flexions. I love to work with rock climbing special attachments for chin-ups and pullups which makes you hold on with 2 or 3 fingers. Think outside of the box to get unconventional results. What I ‘ve seen is when you improve forearm and grip strength, you see immediate transfer on all the other lifts.