Blade broke where to get new one

https://www.lasko.com/products/20-inch-box-fan-b20201/

https://store.laskoproducts.com/p-1005-20-box-fan-model-b20201.aspx

Bex,
THose usually just pull off. You will have to pull hard because there is a spring clamp that they sometimes put around the inside hub of the fan. If there is a clamp, you will need to transfer that to the new blade. Hope this helps!

compressed air

Yes, the capacitor's Voltage rating is the maximum voltage the cap can take. The capacitance value is the important value to consider.

Do you have the still have the e20739 lasko fan, i need the plastic blade on the unit

The motor bearings need machine (like sewing machine oil).
Try a quick spray of WD40 or Liquid Wrench, but use machine oil, soon.
Look for an "oil hole" on top of the motor; there may be two of them.

you need to dismantle the fan.
there are 4 screws under the base
and 16 to the back
top and bottom of the blade is to be oiled
as often as it get dirty.

Joey Temal is right. After removing any small metal retaining clips (which are obvious and easily removed), you have to pull down ridiculously hard to get the fan blade off. Alternate short jerky pulls with steady downward traction.

12,000-BTU Portable Air Conditioner with Manual ... 3135 30-Inch Oscillating Industrial-Grade Pedestal Fan ~ Lasko ... 42.62 : Soleus Air FCM-30 12-Inch Convertible Stand/Table Fan ...

I can tell you how to take the fan blades off your Lasko Model 3723 fan, but you might not be able to use it on your other fan. The reason why is that the motors, although similar, may not have the same diameter shaft.

Of course, you should have the power cord unplugged from the AC outlet before removing the front fan grille and placing your hands on the blades. Safety first!

The fan blades and hub are a single unit that stretches to fit onto the motor shaft. There is no setscrew at all. Take any sort of metal bar or tool such as a screwdriver or pry bar and carefully lever the hub off the shaft by pressing your lever to lift the hub a small fraction of an inch on each side, working the hub slowly upwards against the long vertical bars that support the motor. If you have reasonably strong hands, you may be able to pull the hub toward you by placing your fingertips under the edge of the hub and pressing with your thumbs against the vertical support bars as needed. It's not too difficult to do.

Good luck!