Hi folks, I found a site that shows two different types of serving mallets and a brief description of their use:
Please check:
nautical repair equipment
near the bottom of the page
The use I'm familiar with is to worm, parcel and serve a splice in ropes, cable, ect.
Worming was to lay a small filler cord into the grooves on a larger cable or rope to give a more even, round size and eliminate pockets between the parceling and the cable.
Parceling was when tarred paper or canvas strips were wrapped around the cable securing the worming. this was done much like wrapping electrical cables with vinyl tape.
Serving was to wrap the entire length of the splice with a smaller cord to secure everything else and add strength to the splice.
worm and parcel with the lay, but always serve the other way.