For a center post or where you do not need additional side posts, cut a 1 1/2 inch notch in the deck post to the combined height of the rim joist and the thickness of the deck flooring material.
Figure 4 - Railing post notch
For an end post where you want or need outside posts along the width of the deck, the corner post is notched to allow the same thickness on both the width and length of the deck framing, as shown in Figure 5.
Figure 5 - Corner & mid railing post notch
Note: Some installations will have the deck post notch resting on the rim joist. This means that the deck flooring must be cut around the deck post. I prefer to have the deck post notch resting on the deck flooring.
Apply some wood sealer to the inside of the notch and to the rim joist area that will be hidden by the deck post. This will help to prevent rotting from occurring between the rim joist and the deck post and hence, extend their life.
If you are using lag bolts. Drill a 3/16 inch pilot hole through the deck post and into the rim joist. Four bolts should be sufficient. The holes should be symmetrical and be not less than 1 1/2 inches from the bottom of the deck post and not more than 1 1/2 inches from the top of the rim joist. Remove the deck post and drill the deck post to the diameter of the lag bolt 3/8 inch is usually sufficient and drill the correct size lag bolt pilot hole in the rim joist.
Figure 6 - Carriage bolt
If you are using nuts and bolts, I would suggest the use of carriage bolts, as shown in Figure 6, as they provide finished aesthetics are much nicer than hex bolts. Drill a 3/16 inch pilot hole in the same manner as above and then drill out the pilot hole to the thickness of the bolts being used. Always use a flat washer under the nut if you are using a carriage bolt and under the nut and the head if you are using a hex bolt. Four 3/8 inch bolts should be sufficient.
Note: It is best to use stainless steel fasteners. Under no circumstances should you use regular steel bolts outdoors.