Z it might be these.

https://www.cef.co.uk/catalogue/products/4706254-storm-tauras-m20s-cable-gland-2-per-pack

Z.

Made by the aptly named SWA company

https://www.swaonline.co.uk/cable-glands-accessories/armoured-cable-glands/storm-cable-glands/storm-plastic-armoured-cable-glands

They also do the shakeproof washers that almost no-one every bothers to fit with SWA glands.

https://www.swaonline.co.uk/cable-glands-accessories/cable-gland-accessories/serrated-washer

Though how you buy from them I have yet to work out.

Mike.

What cables are they for?

They claim compatibility with armoured so SWA, and braided so SY, CY.

Mike.

I’m inclined to think they are EMC glands.

https://youtu.be/jpoIkMaCwqU

well in the sense they make an all round circumferential connection to the braid or armour, they are  better for EMC than the slotted bolt gland designs that introduce pigtails in the screen path and so are not as good for short pulses/ high frequencies.

Also occurs to me that for TT islanding into a plastic box this is a nice way to get the armour properly clamped and available for testing inside  the box without  the problem of an 'untouchable gland'  and mabye nicer than using a stuffing gland and heatshrink.

Mike