Shimano Part Number: Y3SV98020.
The cone itself works fine as a replacement for Shimano Part Number Y3D698030, (Left Cone/Locknut from Shimano FH-T660) The spacer is 0.4mm thicker, and the locknut 0.5mm thinner according to our measurements so we recommend using your original ones if possible if you're servicing an FH-T660 hub. However, as it's a swings and roundabouts situation, you should be able to replace the complete 3-piece assembly without a problem.
Cone: M10 x 15mm. Weight: 26g.