Please select size from the pull down menu. The insert length is 1.5 x diameter. METRIC Left Hand Size Part # Inserts Per Package 6-1 STRM6x1LH 6 8-1 STRM8x1LH 6 8-1.25 STRM8x1.25LH 6 10-1.25 STRM10x1.25LH 6 10-1.5 STRM10x1.5LH 6 12-1.25 STRM12x1.25LH 6 12-1.75 STRM12x1.75LH 6 14-1.5 STRM14x1.5LH 4 14-2 STRM14x2LH 6 16-1.5 STRM16x1.5LH 4 16-2 STRM16x2LH 4 18-1.5* STRM18x1.5LH 4 18-2.5 STRM18x2.5LH 4 20-1.5 STRM20x1.5LH 2 20-2.5 STRM20x2.5LH 2 22-1.5 STRM22x1.5LH 2 24-2 STRM24x2.LH 2 24-3 STRM24x3LH 2 * M18 extra fine is a different spec and thread form to M 18 Spark Plug For more information please visit: http://www.newmantools.com/sti/stilh.htm