Before the invention of nail guns there was only one kind of framing nail--round-head. Once nail guns came along, companies started clipping nail heads to allow the nails to be placed against each other in the clips and everyone started using them. Round-head nailers started gaining popularity in certain areas and their use is mandated by code in many places.
Clipped-Head Nail Guns
Clipped-head nail guns fire a type of framing nail known as a clipped-head nail. The heads of the these nails are standard round-head nails on the front side, but the back of the head is clipped off flush with the shank of the nail.
They are collated into clips of nails by placing the head of the first nails just under the head of the second nail and so on, with the shanks of the nails touching each other. A specially coated paper strip applied to both sides of the clip keeps the nails in place.
Round-Head Nail Guns
Round-head nail guns fire nails whose heads are completely round, like standard hand-drive framing nails.
The nail clips use paper or plastic strips to collate the nails. Since the heads are fully round, a space must be maintained between the shanks, meaning that the collating straps actually wrap each nail rather than just being applied to the sides.
Clipped Head Advantages
Since clipped-head nails are collated with the nail shanks touching each other, more nails can be placed in each clip, resulting in more nails fired between reload, saving time throughout a day. The magazines for clipped-head nailers tend to be smaller as well, making for a lighter, easier to wield gun.
The other advantage clipped-head nails have over round-head nails is price. Since the collation process is simpler with clipped head nails, the cost to manufacture them is lower than round-head nails.
Round Head Advantages
Round-head nails possess one main advantage over the clipped heads--holding power. Wood nailed with round-head nails is more likely to stay put in high winds or under high torque or pressure loads than clipped head nails since the round heads provide more bearing surface on the wood.
Round-head nails also help prevent overdriving of the nail since they have larger heads and it is harder to sink them into the wood. This is the main reason they are preferred in seismically active and hurricane-prone regions. Overdriven nails in shear walls can lead to building failure under extreme conditions such as an earthquake or hurricane-force winds.
Some dispute these claims, including Senco Tool Company, manufacturers of a wide range of nail guns and nails. According to Senco, laboratory tests show no measurable difference between the two types of nails.
Nails are starting to emerge on the market today with full round offset heads. Instead of the head being centered on the shank, the head is offset to one side, allowing the shanks to touch one another. These nails are designed to be fired in a clipped-head nailer, effectively turning a clipped head into a round-head nailer.
Some jurisdictions, especially in areas subject to sudden bursts of high wind such as hurricanes, don't allow the use of clipped-head framing nails.