The Grease Zerk caps by FSTURIOS came recently (so this is a short term, initial review). There are 8 of them (as advertised), and since I have 2 cars, with 4 wheels, (lol, yes, but wait for it) that likely need a cap at each wheel, this will meet my needs for now. Please be safe working, and note I'm NOT a mechanic, as you hear my experience:Before I did my "installs", though there isn't much to the actual process, I had a sheet of cardboard, to make sitting on the ground more comfortable, and to capture any grease or fluids. I also had paper towels, metric wrenches, a wire brush and some WD-40. I wore old clothes, had gloves on, to better prevent cuts and keep grease from my hands. Then with my car parked on a stable, level surface, put on the parking brake, tire chucks in front and behind of 2 opposite wheels, jacked up my vehicle, and put a jack STAND under the axle / wheel / or jacking points. (See your car maker for exact locations).On a car I just bought, on 1 wheel, after taking the lugnuts off, the wheel was stuck on. So I sprayed WD-40 around the wheel studs (threads lugnuts were on), and gave it 10 minutes to soak in. Then I took a rubber mallet, and forcefully hit the inside of the wheel a few times until it was unstuck. You can also kick at the tire from the inside, but only if you're comfortable the car is jacked up safely. I believe it's most stable to put 2 or 4 wheels on jack stands (not a single wheel), and test it by trying to shake the car. I also kept my hydraulic jack in place, after SLOWLY lowering down most of the weight onto the jack stands, so that I had up to 2 items keeping that corner of the vehicle up. I'm doing 1 wheel at a time, (as I like to keep the other wheels on), BUT, again, I'm still going to jack up each side and put a jack stand under each side, as jack stands won't roll, like a hydraulic jack can. If you only jack up 1 side, the other wheels could potentially roll, which could allow the car to fall in the first place.I have an impact gun and impact sockets to more quickly take my lugnuts off, but of course you could use a socket and ratchet - and when it's time to put the lugnuts back on, I'll start them by hand, and finish w/ a torque wrench to make sure they'll aren't too tight. When doing the zerks on the front, after removing each wheel, I cleaned my hands, and carefully got in the car and turned the steering wheel in the direction that would give me easiest access to them. (Steering turned right for the driver side wheel, and steering turned left for the passenger side wheel.) After finding the grease zerk, I first wiped the outside clean with a paper towel, then cleaned the area with brake cleaner. I have an air compressor, but avoid using it when doing any work around the brakes, as the dust is harmful. Instead, I took the metal wire brush to clean off any dry material or rust. I sprayed each zerk fitting (1 per wheel of course) with WD-40 and wiped off the excess, before actually putting on the round ring of the cap over the zerk first, then folded the cap over the open zerk end. (If you get the ring the right way, the cap will fit. The wrong way, the cap end will be backwards. The WD-40 will help displace moisture (which is bad on brake fluid), prevent rust, and potentially allow the grease zerk to turn when serviced - like for brake bleeding or brake caliper replacement. While I'm at each wheel, and before spraying the WD-40, I will look for any signs of brake fluid loss, and maybe the wear pattern on the disc brake rotors. Often, a vehicle will give you a clue when something is wrong and need repair or maintenance. Even if you cannot fix the car yourself, you may be able to tell when it's time to take to a shop.When the wheels were back on, I removed the chucks from the wheels, and took off the parking brake, lest I forget later. I cleaned my tools with a paper towel before putting them away. Then, I looked to make sure I had not forgotten something. Job well done.

The opening is 6mm in diameter. Too small for an 8mm fitting.