A fid is a conical tool made of wood or bone. It is used to work with rope and canvas in marlinespike seamanship. A fid differs from a marlinspike in material and purpose. A marlinespike is used in working with wire rope, may be used to open shackles, and is made of metal. A fid is used to hold open knots and holes in canvas. A fid is used to open the "lays", or strands of rope, synthetic or natural, for splicing said line. A variation of the fid, the Gripfid, is used for ply-split braiding. It adds a jamming cleat to pull a cord back through the cord split by the fid's point.
The term has wider nautical use: e.g. "A little iron fid drops into a slot in the stock (of an anchor)to keep it in place"[1]
In the Canadian Navy, "fid" is also used as a euphemism for a stupid person.
A "fid" is also a unit of measurement equaling approximately 21 or 22 times the rope's diameter. The fid is further divided into a "short" fid and a "long" fid. A short fid is 1/3 the length of the full fid and a long fid is 2/3 the length of the full fid.
This chart shows examples of short, long, and full fid lengths for ropes of almost all diameters.
Fids may come in other shapes, diameters, and lengths, some solid and others hollow. Other than wood, they may also be made of titanium, stainless steel, aluminum, brass, bronze, or copper.
| Rope Diameter (in.) |
Rope Circ. (in.) |
Short Fid (in.) |
Long Fid (in.) |
Full Fid (in.) |
| 3/32" | 9/32" | 2/3" | 1⅓" | 2 |
| 1/8" | 3/8" | 7/8" | 1¾" | 2⅝" |
| 5/32" | 15/32" | 1 | 2-1/5" | 3-2/7" |
| 3/16" | 9/16" | 1⅓" | 2⅝" | 4" |
| 7/32" | 21/32" | 1½" | 3" | 4-3/5" |
| 1/4" | 3/4" | 1¾" | 3½" | 5¼" |
| 9/32" | 27/32" | 2" | 4" | 6" |
| 5/16" | 1" | 2-1/5" | 4⅜" | 6-4/7" |
| 3/8" | 1⅛" | 2⅝" | 5¼" | 7⅞" |
| 7/16" | 1¼" | 3" | 6⅛" | 9-1/5" |
| 1/2" | 1½" | 3½" | 7" | 10½" |
| 9-16" | 1¾" | 4" | 7⅞" | 11-4/5" |
| 5/8" | 2" | 4⅜" | 8¾" | 13⅛" |
| 11/16" | 2¼" | 4-4/5" | 9⅝" | 14-4/9" |
| 3/4" | 2¼" | 5¼" | 10½" | 15¾" |
| 7/8" | 2¾" | 6⅛" | 12¼" | 18⅜" |
| 1" | 3" | 7" | 14" | 21" |
| 1⅛" | 3½" | 7⅞" | 15¾" | 23⅝" |
| 1¼" | 3¾" | 8¾" | 17½" | 23¼" |
| 1-5/16" | 4" | 9-1/5" | 18⅜" | 27-4/7" |
| 1½" | 4½" | 10½" | 21" | 31½" |
| 1⅝" | 5" | 11⅜" | 22¾" | 34⅛" |
| 1¾" | 5½" | 12¼" | 24½" | 36¾" |
| 2" | 6" | 14" | 28" | 42" |
| 2⅛" | 6¼" | 14⅞" | 29¾" | 44⅝" |
| 2¼" | 7" | 15¾" | 31½" | 47¼" |
| 2½" | 7½" | 17½" | 35" | 52½" |
| 2⅝" | 8" | 18⅜" | 36¾" | 55⅛" |
| 2¾" | 8½" | 19¼" | 38½" | 57¾" |
| 3" | 9" | 21" | 42" | 63" |
| 3¼" | 10" | 22¾" | 45½" | 68¼" |
