Galvanised Nails have been coated after manufacture with zinc for corrosion protection. For exterior use or where moisture may occur.

Handy Tips – Smooth Shank Nails / For Common Fixing
A rule of thumb that can be used for determining the length of nail required is three times the thickness of the timber being fixed. e.g. 25mm Timber = 75mm Nail.
Stagger nails where close nailing is necessary to prevent timber splitting.
When nailing near the edge of the work surface it may be necessary to drill pilot holes using a slightly smaller diameter drill than the nail shank to stop the timber splitting.
Wherever possible, skew nail to maximise joint strength.

Flat Head nails have a large diameter head (normally up to 2.5 times the thickness of the nail shank). This head will sit slightly proud of the work surface. Flat head nails are designed to resist pull through on soft or thin timbers. This nail is used where the concealment of the head is not critical.