V-belt, in between variator/stern belt. Common in riding mowers manufactured by MTD.

Suitable for example:
Cub Cadet LT1018-LT1529
MTD 600 series riding mowers from 2003 onwards
MTD 13A1662F600
MTD 13AA668F678
MTD 13AA668G678
MTD 13AA688G678
MTD 13AC660F647
MTD 13AH650F752
MTD 13AH662F600
MTD 13B1662F60
Stiga SD12.5-96 2005

Replaces original numbers:
Cub Cadet 754-04002
Cub Cadet 954-04002
Husqvarna 578453624
MTD 754-04002
MTD 954-04002
Oregon 75-709
Ratio Parts 008-102
Stiga 20001253 /0
Stiga 1132-2211-01
33-407-34
39-646

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A wide selection covers spare parts and accessories for lawnmowers and chainsaws.