Ken - fist - knuckles

Though we tend to think of the word "ken" as meaning "sword", as in Kendo and Kenjutsu, (even though the Japanese word for sword is actually "To") in Karate we use the word Ken to refer to our physical weapons or striking tools.

The word ken perhaps best translates to the English word "fist" or "knuckles".

When making a strike it is vital to be aware what Fist you are making and what knuckles you are hitting with.

Make a clenched fist and you have a Fudoken.
With this you might do a boxing cross using the first two knuckles
or a Wing Chun choy and use the bottom three.

Shuto is the knife hand. As well as the fleshy part, you have a knuckle at the base, the pisiform bone.

Haito - the ridge hand, using the index knuckle.

Koppo Ken - the thumb knuckle

Uraken - the backfist.
You'd be surprised how many people, having trained extensively in pads, actually think you hit with the back of the hand. Good way to break the metacarpals on the opponent's skull.
Use the back of the first two knuckles of fudoken.

Palm heel - heel of the palm, obviously.

With the long bones such as the elbow, knee or shin - well, we've all seen the cartoon dog holding a bone in it's mouth, with the nobbly ends. It's these nobbly ends we're using as "knuckles".
The elbow, knee and shin kick use the knuckle at the end of the ulna, femur and tibia respectively.

When kicking with the foot, use the knuckle of the foot, not the laces. If you have steel caps on, this makes your shoe a weapon.

Koshi is the ball of the foot.

The heel is the bottom of the heel, like in a stamp.

Head. The general rule for a headbutt is the line above the eyebrows is the weapon and the line below the eyebrows is the target.

The Japanese name for he head as a weapon is kikaku ken. But another term is zu tsuki meaning horn thrust. Imagine you have horns on your forehead, like a bull. Use one of those. Forward, down, sideways or up.