Pella 818K0100 Installation Instructions Manual page 11

Secure the jambs and head of the door.
DO NOT
Drill 13/64" clearance holes through the threshold
Installation Clip Method:
Fasten the door to the opening by driving two #8 x 1-1/4"
Frame Screw and Installation Clip Methods:
Drive #10 x 3-1/2" corrosion resistant wood screws
5D
5C
5F
DO NOT