This is part number 5534468000 which is equivalent to 50123830 and variants without trailing zeros. TEAC X3 X3R X300R A2300 A3300 A3340 A4300 A6100 A6300 A3440 80-8, 40-4. These are new production, from TEAC.
NEW TEAC OEM Capstan Belt 5534692001 X-7R X-10R X-20R X-1000R X-2000R A-4010/S
This is part number 5534692001. TEAC X-7R, X-700R, X-10R, X-20R, X-1000R, X-2000R, A-4010. These are new production, from TEAC.