[NN5I]

Actually the question was mostly rhetorical, the intent of the message being in the nature of Adlai Stevenson's remark, A funny thing happened to me on the way to the White House ...

Still, lexicographic mysteries exist to be solved. Bibbs, it appears, are used specifically in the structure (at the top of, for example, a mainmast) that supports and holds vertical an additional section of mast (a topmast), which may in turn have similarly attached to its top end a topgallant mast.

The illustration shows bibbs and trestletrees, from an article on model-building.

Note that the dimensions shown seem small; they are for a model of a tall ship.

The topmast attaches to the front face of the mainmast at the head, and the topgallant mast (if present) to the front face of the topmast at its head. If the ship is really tall, or the builders hail from a place with no tall trees, it may have a royal mast above the topgallant.

The bibbs are securely fastened to the sides of the mainmast (to the hounds [see below]) as shown; then the trestletrees sit on the bibbs and extend fore and aft. The crosstrees are longer; they sit on the trestletrees and extend athwartship. The topmast sits on the crosstrees and is fastened to the head of the mainmast.

A hole extends fore-and-aft through the mainmast and topmast. Through this hole, which aligns when the topmast sits on the crosstrees, is placed a timber (or a metal piece) of square or rectangular cross-section, the fid, which is loaded in nearly pure shear and supports most of the vertical load (weight of the topmast and its attachments, plus the resultant of the tensions on the rigging).

Then considerable additional structure is added, supported by the nice long crosstrees, to give men a place to stand and to provide attachment points for the rigging and so forth.

The mast shown in the illustration apparently has no hounds, which would be a layer of timber enclosing (on all four sides) the part of the mast to which the bibbs and topmast are fastened. In the model, the masthead is squared by cutting; on a tall ship it is squared by adding the hounds, which are timbers that are shaped to fit the mast on one side, and flat on the other for attaching the bibbs etc. Thus the mast is strengthened, instead of being weakened, to create flat attachment surfaces.

Two days ago I knew none of this. I think I have it mostly right.