These guide bar cover nuts are a M8 thread, use a 19mm spanner and fit the 009, 010, 011, 017, 018,020,021, 023, 025, 026, 028, 029, 030, 031, 032, 034, 036, 038, 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, MS381, MS390, MS391, MS440, MS441, MS460, MS640, MS650, MS660 & MSE200C.