KARACHI, Pakistan, Feb 9 (Reuters) - The Karachi Cotton Association on Friday fixed the official spot rate, or base price, for Grade 3 cotton at 7,502 rupees per maund (40 kg). Grade 3 cotton has a staple length of 1-1/16" and micronaire value between 3.8 and 4.9 NCL (no control limits), which represents fine to coarse classes of cotton varieties. In the kerb market, the key crop varieties traded in the range of 7,000 to 6,400 rupees per maund. The following are the grade and staple margins for Feb 1 to Feb 15, 2018: GRADE 31/32" 1" 1-1/32" 1-1/16" 1-3/32" 1-1/8" Super n/a n/a n/a n/a n/a n/a 1 n/a -322 0 322 536 750 2 n/a -482 -161 161 375 589 3 n/a -857 -429 BASE 214 429 4 n/a -1179 -750 -322 54 268 5 n/a -1500 -1072 -643 -107 107 (Reporting by Syed Raza Hassan)