Rule In-Line Blower 3". Compact and easily installed on any flat surface Rule? in-line blowers provide higher air flow lower amp draw and quieter operation than standard blowers. For International & US Markets. Specifications for Rule 3" In-Line Blower: Manufacturer: Rule Color: Black Voltage: 12 volts Features of Rule 3" In-Line Blower Ducting: 3 Open Flow (CFM): 135 Volts: 12 Package Contents: Rule 3" In-Line Blower Rule 140: In-Line Blower 3"