3/8" holes and into the wood studs. Just seat the screw, don't over tighten. After you get the screws into the sides and top, remove the sliding panel. The bottom track should lift out. Look for drainage holes in the track and insert a thin screwdriver and lift up. Drive one screw in the bottom center, caulk around the screw head, then put the track back in place and re-install the sliding panel. Now, you want to go back outside and caulk the gap where the retrofit fin meets the exterior surface of the house. You want to have a double barrier of protection against water infiltration. Remember, you already applied a generous bead of caulk before inserting the new frame into the opening. The rest of the job is done on the inside.First, you want to plug the 3/8" screw holes to hide the heads of the screws. We sell the hole plugs on the website. Just click on the "shop" tab to see a picture. The plugs will pop into place in the hole. The next step is to fill the gap around the new frame with R-13 Insulation. Do not use the foam insulation that comes in a can. Many manufacturers will not honor the warranty if the foam is used. Even the non expanding foams can cause the frame to distort, causing problems. Pack the insulation in tight. You might want to wear a dust mask during this procedure. Many people, myself included, are very sensitive to insulation. After the insulation is in place, you want to install trim around the inside to finish the job. You can use wood trim from the hardware store, or some other product. But in my experience, the best product is a vinyl flat trim that matches the window frame. The flat trim can also be purchased on the website under the "shop" tab, or you could try to find it from a local window contractor. Ours comes in 3 different widths, although the 1 3/4" wide piece is by far the most common. The trim has a double sided adhesive tape on the back. You cut the top and bottom first, stick them on the vinyl frame, making sure the trim goes to the drywall. This covers all the insulation and the old metal frame. Do the side pieces next. The final step is to caulk where the trim meets the walls.Much of the installation process for a replacement frame is the same as the retrofit frame. But, there are a few differences. When you put the new window into th