LONDON, May 21 (UPI) -- Closing bid and ask prices on the London Metals exchange Friday: (quoted in U.S. dollars per metric ton): Bid Ask Copper grade A Cash 1477.50 - 1478.50 3 mths 1509.00 - 1509.50 15 mths 1585.00 - 1595.00 Tin Cash 5690.00 - 5700.00 3 mths 5690.00 - 5700.00 15 mths 5605.00 - 5615.00 Lead Cash 547.00 - 548.00 3 mths 547.00 - 547.50 15 mths 538.00 - 543.00 Zinc special high grade Cash 1031.00 - 1032.00 3 mths 1052.00 - 1052.50 15 mths 1065.00 - 1070.00 London silver large Cash 5.2200 - 5.2400 3 mths N/A - N/A 12 mths N/A - N/A Aluminium high grade Cash 1317.00 - 1318.00 3 mths 1342.00 - 1343.00 15 mths 1397.00 - 1402.00 Nickel Cash 5390.00 - 5400.00 3 mths 5465.00 - 5470.00 15 mths 5645.00 - 5665.00 Aluminium alloy Cash 1237.00 - 1240.00 3 mths 1252.00 - 1253.00 15 mths 1285.00 - 1305.00  