As stated previously, chainsaw vibration will undo screws on some climbing devices. And intensive use (production tree climbing) is also likely to exacerbate the problem.
Further to the previous discussion, a flurry of social media comments regarding loose screws on the Petzl Sequoia lower D's (securing the bridge to the harness) has surfaced.
Most social media commentators blame Petzl for the screws undoing as if it's a design fault. But remember, there are multiple products in the Petzl portfolio with screw attachments; Ring Open, ASAP Lock, Astro, Eject, Micro Grab, Chicane, MGO and Eashook Open, Swivel Open, Trac, and Sequoia harnesses. Adjustment screws mean greater versatility for the user (better value for money), but there is a trade-off for the advantage; you, the user, must maintain the gear.
Petzl is not the only manufacturer to go down the versatility path using screw connections; it's simply a modern design requirement for gear (think DMM with the Nexus and Focus Swivels and the Director series of connectors).
The Petzl screws have a small O-ring close to the head, which helps secure the screw in position.
If you can see the red O-ring once seated, the screw is not tight enough.
Checking the tightness of the screw should be part of your regular PPE inspection. However, an intensive user (e.g. aerial arborist) may require more frequent PPE inspections, especially the screws' tightening torque. A torque wrench is the only way to verify that the tightened torque is correct.
Some climbers advocate using a thread locker (Loctite), which is all well and good but depending on your choice of thread lock, disassembly may become difficult or impossible. And, there is a possibility the 3mm Hex head screw will round off if you are too aggressive with your actions. But, again, Petzl provides instructions on the correct procedure if you are unsure.
The Petzl screw discussed above is necessary if you want the benefit of a field-replaceable bridge. However, if maintenance is not your bag and you worry about the screw undoing, purchase a harness without a replaceable bridge, but your options will be limited.
