When measuring to form a tail that’s to be a hook shank in length, begin by aligning the tips precisely at the start of the hook bend. Then squeeze the fibers between the thumb and index finger of your left hand to hold them in that position. Place your right hand thumbnail at the back edge of the hook eye to measure out the shank length. Then transfer the measurement rearward to the start of the bend. Using your nail is generally more accurate then just your fingertip. You can then secure the tail with thread wraps back to the start of the bend. You should be left with a tail exactly as long as the hook shank.
A hook-shank-long wing can be produced in a similar manner. Align the tips with the back edge of the hook eye and mark the shank length with the thumbnail of your left hand. Transfer the measurement forward to the tie-in point. There, using the edge of your thumbnail as a guide, start taking thread wraps to anchor the wing material to the top of the hook shank. This should result in an accurately placed wing that’s precisely a hook shank in length.