You need:

Flexible straws 5.0 - 5.5 mm in diameter (thick straw)

Flexible straws 4.0 -4.5 mm in diameter (thin straw)

3 strips of 6 mm x 8 cm insulation tape

A paper windmill sheet (please cut along the solid lines and make five holes using a one hole punch or a cork borer)

Cut a thick straw into 8 cm. and apply one of the 6 mm x 8 cm insulation tape strips near one of the ends of the straw.

Pass the free end of the 8 cm straw through a hole in the middle of the paper windmill sheet.

Pass the straw end through blade holes one by one.

All the blade holes passed through the straw.

Apply the second insulation tape strip near the free end of the 8 cm thick straw.

Your windmill blades are ready.

A thick straw has a short arm, a flexible part and a long arm.

Trim off the short arm to make the short arm about 2 cm long.

Stretch the flexible part of the thick straw.

Take a thin straw and stretch the flexible part.

Insert the long arm of the thin straw into the thick straw’s long arm, until the long arm of the thin straw comes out from the opposite end of the thick straw.

Pull the thin straw to overlap the flexible parts.

Give a push to both straws to shorten the both flexible parts.

Gently fold the both straws to make a right angle like the right image.

Insert thin straw into the windmill blade thick straw.

Apply the third insulation tape strip like the photo above.

Trim off the thin straw.

Your paper windmill is completed.