KARACHI, Feb 6 (Reuters) - The Karachi Cotton Association on Friday fixed the official spot rate or base price for Grade 3 cotton at 5,198 rupees per maund (40 kg). Grade 3 cotton has a staple length of 1-1/16" (inches) and micronaire value between 3.8 to 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 4,625 to 5,100 rupees per maund. Following are the grade and staple margins for February 1 to 15: 31/32" 1" 1-1/32" 1-1/16" 1-3/32" 1-1/8" Super -375 -268 -54 +268 +429 +536 1 -429 -322 -161 +214 +375 +482 2 -482 -375 -214 +161 +322 +429 3 -643 -536 -429 BASE +214 +322 4 -1072 -965 -857 -429 -214 -107 5 -1179 -1072 -965 -536 -322 -214 (Compiled by the Karachi newsroom)