Checking the grip when holding the bokuto.
We should have a feeling of “shime” (squeezing) our grip slightly inwards when in ken no kamae - like wringing a cloth. This brings the hands into a position where the first two knuckles of each hand are visible (to yourself).
Our grip should feel connected to our center/hips/hara/koshi/tanden.
When we grip in aikido in general, and in weapons work as well, we should be gripping by closing the grip with the “inside” - meaning holding strongest with the pinky and ring finger. This centers the grip, activates the “inner” or lower muscles of the forearm and the triceps in the upper arm, and connects the grip to your hips.
If you close the grip by using the index and middle finger, you will be activating the “outer” muscles - meaning the “top” muscles of your forearm and the bicep of your upper arm. This brings tension upwards into the shoulder and neck, and doesn’t create a connection to the hip, all of which which is detrimental to what is needed in both weapons work as well as in tai jutsu.
In ken no kamae: you can see if the grip is being done properly by looking at the position of the thumb: if the thumb of the front hand (and the rear hand, too) is pointing straight down, it is because the grip is being closed incorrectly; by using the index and middle finger. Another indicator is if the index finger is also pointing straight down.
If done correctly, the thumb will be at a natural angle forward, as will the index and middle finger.
In the correct position, if you release the hand from the weapon and keep the same position while opening the fingers, the hand will be close to being in the tegatana position.
If you hold with the incorrect grip, and you release the hand from the weapon and extend your fingers, your hand will be in a position that does not belong to the hand positions that are used in aikido.
I recommend trying this - you should be able to feel the difference quite easily.