Solve the following sql problem:
How many customer ids have purchased Hex Nut 9?

Schema:
SCHEMA:
- Table: Customers
  - Column: CustomerID
    - Samples: [1, 2, 3, 4, 5]
  - Column: FirstName
    - Samples: [Aaron, Aaron, Aaron, Aaron, Aaron]
  - Column: MiddleInitial
    - Samples: [None, None, None, None, None]
  - Column: LastName
    - Samples: [Alexander, Bryant, Butler, Chen, Coleman]
- Table: Employees
  - Column: EmployeeID
    - Samples: [1, 2, 3, 4, 5]
  - Column: FirstName
    - Samples: [Abraham, Reginald, Cheryl, Michel, Innes]
  - Column: MiddleInitial
    - Samples: [e, l, a, e, e]
  - Column: LastName
    - Samples: [Bennet, Blotchet-Halls, Carson, DeFrance, del Castillo]
- Table: Products
  - Column: ProductID
    - Samples: [1, 2, 3, 4, 5]
  - Column: Name
    - Samples: [Adjustable Race, Bearing Ball, BB Ball Bearing, Headset Ball Bearings, Blade]
  - Column: Price
    - Samples: [1.6, 0.8, 2.4, 0.0, 189.6]
- Table: Sales
  - Column: SalesID
    - Samples: [1, 2, 3, 4, 5]
  - Column: SalesPersonID
    - Samples: [17, 5, 8, 1, 14]
  - Column: CustomerID
    - Samples: [10482, 1964, 12300, 4182, 15723]
  - Column: ProductID
    - Samples: [500, 306, 123, 437, 246]
  - Column: Quantity
    - Samples: [500, 810, 123, 437, 750]

SELECT COUNT(T1.CustomerID) FROM Sales AS T1 INNER JOIN Products AS T2 ON T1.ProductID = T2.ProductID WHERE T2.Name = 'Hex Nut 9'