This particular model of adapter allows you to use lenses which do not have a dedicated aperture ring. These adapters do not have any electronic connection to the camera and hence cannot "tell" the camera what aperture is set, therefore the adjustable ring on the adapter provides a means of manually adjusting the amount of light passing through the lens to the camera sensor. NB If you have lenses WITH an aperture ring you could use another simpler (and cheaper} model of adapter and manually adjust the aperture on the lens. 

I have the X-T4, but the X-T3 and X-T4 both have the same sensor and lens mount, so the adapter should work with both equally well. You need to be aware though, that there are no electrical contacts, so Pentax lenses that do not have an aperture ring will not have any way of controlling the aperture setting. I think the mount adapter is well made and good value for money. 

Don’t forget that it’s a manual lens adapter. Works with full manual lenses. If your lens has no physical aperture ring, you cannot control it from your camera 

No Allen wrench comes with the unit and I did not need one. Mine did not require any adjustments and fit like a glove. 

Hi, this adapter is for Canon EOS mount lens to Sony E NEX mount camera, we checked the sony a 7iii camera mount is E mount , this adapter can fit it , but you can reconfirme it , thanks. 

Yes, it is indeed Nikon f mount. 

Hi, this adapter is for Canon EOS mount lens to Sony E NEX mount camera, we checked the sony a 7iii camera mount is E mount , this adapter can fit it , but you can reconfirme it , thanks.