Muffin fans, pay attention. You pick the "nice" 110 VAC 21W fan from Thermocool, measuring 4-3/4" square x 1-1/2" thick with an offset two-pin power connector, rated for 82-95 cfm and spinning at approx 2600 rpm, with five blades and 3/16" mounting holes at the corners (Mfr part # G12038HA1ST); or the "beastly" 110VAC 36W muffin fan from the same mfr, which blows up to 198 cfm at 2900 rpm and measures 6-3/4" x 6" tall x 2" thick with (2) power terminals on a removable shroud, 5 blades, 5/32" mounting holes on the corners plus a ground lug. Both UL.

Our special Little-Fans-R-Us offering. All these muffin fans are square and all have mounting holes at the corners. Pick and choose the one you want or take a chance on the takeout assortment. (Assortment will not have fans listed in the table above) Please note that the assorted fans are takeouts and will have at least have least two different fans from different manufacturers but maybe the same size. It will be a crap shoot as to what you will receive. 

And even more fan blades. Choose a white-plastic 5-blade or a black-plastic 4-blade, each approx 4" across with a 3/16" bore. Designed for clockwise rotation. No motor. Just blades. (But nice little blades.)

Thin, too. This impedance-protected muffin fan from Sunon is 4-5/8" sq x 1-1/2" thick. It has (5) blades and is rated 115VAC, 240mA and 117CFM. It might even come with a 2-foot jumper cord. Mounting holes in the corners.

This 12VDC low-pressure, piston-driven, diaphragm air pump has a 7/32" inlet. Motor draws 100mA no load, stalls at approx 4.3A, spins approx 3500 rpm and measures 4" x 1-5/8" x 3" with 10" leads. Shaft has a 1/2" dia cam to drive the piston. Motor is Mabuchi RK-555PH.

This little L-shaped low-pressure piston-and-diaphragm air pump has a 7/32" OD inlet and an 11/32” OD x 9/32” ID outlet, and is attached to a Mabuchi RK-555PH 12VDC motor that draws 100mA no load, stalls at 4.3A, and spins approx 3500 RPM. Measures 4" x 1-5/8" x 3" with 2” leads.

This 12VDC muffin fan from AVC® draws 700mA and blows approx 42cfm. Measures a cute 2-3/4” square x 1/2” thick with (9) curved blades, a 4-pin connector and 8” leads. Use red and black leads for power. The other two we believe to be a tachometer. Part #DE07015B12U.