Why on earth does a #4 Phillips even exist?

You usually see those #4 Phillips bits in heavy commercial door hardware and steel framing. If you're hanging hollow metal frames into masonry or heavy-gauge steel studs, the expansion anchors often come with a massive cross-head. I’ve had to use them when setting commercial door closers or panic bars too. The fasteners are huge, so a standard #3 would just spin and strip the head immediately. Even then, you have to put your entire body weight behind the drill to keep it from camming out. It is definitely a relic of a different era of engineering. Back before Torx and Robertson became the standard for high-torque applications, the Phillips design was actually intended to cam out so that assembly line workers wouldn't over-tighten screws and snap the heads off. In a modern shop or on a residential site, that's just a nuisance, but in a factory setting sixty years ago, it was a feature. But once you get to a fastener size that requires a #4, that 'feature' becomes a total nightmare because of the sheer force needed to stay seated. Most people mistake a large **PoziDriv** (PZ4) for a Phillips #4, which is common in European machinery or heavy automotive components. You can tell the difference by looking for the small 'tick' marks or a second cross-shape offset at 45 degrees between the main flutes. If you try to use a Phillips bit on a PoziDriv screw, it’ll strip before you even get it flush. They look similar but the internal geometry is different enough to ruin your day.

Honestly, there is a reason you don't see them in your everyday kit. Most manufacturers have moved to 5/16" or 3/8" hex heads or large **Torx T40** drives for anything that big because they can actually handle the torque without destroying the bit. Unless you’re doing specialized commercial installs or working on old industrial equipment, that #4 is basically just taking up space in your bag. I keep one in my 'just in case' drawer, but it hasn't seen the light of day in five years.

Are you sure it's actualy a #4 Phillips and not a large JIS bit? Have you ruled out old Japanese machinery or vintage motorcycle hardware? I’ve seen people complain about the cam-out on those big cross-heads for years, only to realize they were using the wrong standard for the fastener. If you haven't checked for the little dot on the screw head, you might just be fighting a compatibility issue rather than a design flaw. I rarely see them in framing, but they're still out there in wierd niches.

I’ve run into those #4s mostly on heavy-duty hinges for old-school timber frames or when I’m refurbishing vintage machinery. If you ever find a set of antique Hettich or Blum hardware from a specific industrial era, you’ll see them. I keep a Wera 851/4 Z #4 in my toolbox just for those rare 'oh no' moments. usally, people try to cheat with a #3 and end up turning the screw head into a crater. If you’re driving into somthing like seasoned White Oak with a fastener that size, you better be using an impact driver with some serious nuts, or you're just asking for a wrist-breaker.

While it is certainly true that commercial door hardware remains the primary haunt for these behemoths, I have occasionally encountered the elusive #4 Phillips while restoring mid-century industrial woodworking machinery, specifically when addressing the oversized countersunk machine screws that secure heavy cast-iron tabletops to their internal steel chassis. If you find yourself needing to actually utilize that bit, I would strongly advise verifying that you aren't actually looking at a Frearson drive, wich possesses a sharper 75-degree V-shape compared to the Phillips' 57-degree angle, becasue even a slight mismatch in the recess geometry will inevitably lead to the aforementioned cam-out issues you rightfully dread.