How to Install a New Door Jamb | how-tos | DIY- what type of nails for door casing ,Nail Up the Casing Trim Boards. Next, nail up the outside casing trim. These trim boards are cut slightly narrower than the plinth block and secured to reveal about 1/4" of the side jamb. Install the casing trim. Space the nails about 12" apart (Image 1). To match the top casing trim on the other doorway, a flat 1/4" by 1-1/2" piece of ...Understanding Nail Sizes and Basic Types - The Spruce7/1/2021· Casing and finishing nails are similar, differing primarily in the shapes of their heads. A finishing nail has a small, slightly rounded head that is just slightly bigger than the nail shank. The head is designed to accept the pointed tip of a nail set, making it easier to countersunk the nail without slipping and gouging the wood.