Great Britain made many types of coins but the one closely associated with pirates was the famous guinea. A guinea was worth about a British pound and was named after the West African gold-mining region of Guinea. The coins circulated in the American colonies where the value of the coin was not constant. They are mentioned several times in Robert Louis Stevenson's novel Treasure Island.

Gold, 25 mm, 8.24 gm
Obverse:
George II facing left
GEORGIVS II DEI GRATIA (George II, by the Grace of God)
Reverse:
Crowned arms of Britain, Ireland, France, and Hannover
M.B.F.ET.H.REX.F.D.B.ET.L.D.S.R.I.A.T.ET.E 1750 (The legend is explained below)

Gold, 25 mm, 8.37 gm
Obverse:
George III facing right
GEORGIVS III DEI GRATIA (George III, by the Grace of God)
Reverse:
Crowned arms of Britain, Ireland, France, and Hannover
M.B.F.ET.H.REX.F.D.B.ET.L.D.S.R.I.A.T.ET.E 1794 (The same legend as the George II guinea)

Silver, 27 mm, 2.75 gm, Catalog: Seaby 2561, Third Issue (1561-1577)
Obverse:
Crowned head facing left
ELIZABETH D G ANG FR ET HIB REGINA
(Elizabeth by the Grace of God England France and Ireland Queen)
Pheon symbol (downward arrow at top, London Tower Mint)
Reverse:
Long cross and shield with arms of England and France
POSVI DEV ADIVTOREM MEV (I have made God my helper)

Silver, 31 mm, 5.84 gm
Obverse:
Crowned head facing left
CAROLVS.D:G:MAG:BR:FR:ET:HI:REX.
(Charles, by the Grace of God, King of England, France and Ireland)
Value XII behind, no inner circle, bell mark
Reverse:
Shield
CHRISTO AVSPICE REGNO (I reign under the auspices of Christ)

Silver, 33 mm, 14.30 gm
Obverse:
Charles II facing right
CAROLUS II DEI GRATIA
Reverse:
Four crowned shields of England, Scotland, France, and Ireland
MAG BR FRA ET HIB REX (Great Britain, France, and Ireland, King), year at top

Silver, 40 mm, 29.70 gm
Obverse:
Charles II facing right with rose below
CAROLUS II DEI GRA
Reverse:
Four crowned shields with the combined arms of England and France at top and bottom,
shield of Ireland to left and shield of Scotland to right
MAG BR FRA ET HIB REX (Great Britain, France, and Ireland, King), year at top

Copper, 27 mm, 6.17 gm (An actual halfpenny should be 28 mm and 9.3 gm)
Obverse:
George III facing right
GEORGIVS III REX (George III King)
Reverse:
Crowned harp
HIBERNIA 1775 (Ireland)
These coins circulated in early America.