These quality non genuine guide bar cover nuts are a M8 thread, use a 19mm spanner and fit the 009, 010, 011, 017, 018,021, 023, 024, 025, 026, 028, 029, 030, 031, 032, 034, 036, 038, 039, 041, 042, 044, 046, 048, 064, 066, E20, E220, MS170, MS171, MS180, MS181, MS200, MS200T, MS210, MS211, MS230, MS240, MS250, MS260, MS270, MS271, MS280, MS290, MS291, MS310, MS311, MS340, MS341, MS360, MS361, MS362, MS380, MS381, MS390, MS391, MS440, MS441, MS460, MS640, MS650, MS660 & MSE200C Stihl chainsaws.