The following information is courtesy of Robert Lawrence of Brewer, Maine.

Tho-shot may also be spelled thorough-short or thorough-shot.  It is a wooden pin used to secure log booms for log drives.

Here are a few references to this item:

Lawrence states "Over the years, when fishing, canoeing, etc., I have found several tho-shots, in various lengths.  The longest and largest I ever found was on the East Branch of the Penobscot River (several miles above Whetstone Bridge).  I assume large heavy duty shots were needed because the boom logs on the river would be large and heavy due to the strong river currents during the spring drives, creating tremendous pressure against the booms.  The one you currently have at the Museum is one of the smallest I have ever seen.  Undoubtedly, it was used on a lake or small stream log boom.  The two I have left are rather small and both were found on drained lake bottom."

A description of the museum's tho-shot may be found in the Davistown Museum Maritime III Collection.

Blodgett, Wentworth P. (March 1964). Thoroughshot and boom auger. The Chronicle.
We suggest you check the Mast Trade bibliography and under loggers and sawyers in the Toolmaking Trades bibliography.

A genealogy web page containing a description of using a thorough shot at the Eau Claire saw mill.

Information files:
The museum also has an information file on lumbering in Maine.