The traditional brass gland is still the norm for SWA cables I think - in either BW or CW types depending whether a seal to the outer sheath is required (e.g. for outdoor situations). There as some semi-plastic alternatives these days - e.g. https://www.tlc-direct.co.uk/Products/TLST20S.html but I've no personal experience of them

Where the armour doesn't need a connection or is terminated in some other way, plastic stuffing glands are sometimes used (although in situations like a TN supply to an outbuilding which is a TT island, there's usually a need for the end of the armour to be electrically accessible for testing, so often a brass gland is still used - if into a plastic enclosure).

As for sizing, I've never found any definitive standard - each cable and gland manufacturer seems to have their own slightly different way of doing things. The thread size (20, 25, 20S etc) not being consistently relatable to the cable size across manufacturers. As there also some manufacturing tolerances in the overall cable diameter,  I've even seen some suggestions that the actual cable diameter should be measured on site to select the correct gland size. Most packs of glands come with a table of gland sizes to cable sizes.

"Earthing nuts" (e.g. https://www.tlc-direct.co.uk/Products/PRPEN20.html) can be very useful where terminating into an enclosure wall that can't be relied upon for PE continuity to the gland (e.g. plastic boxes).

    - Andy.

Thanks for your valuable reply!!

If you could suggest some good hole saw cutter for making cable entry holes in electrical panels, it would really help a lot. 

Thanks for your valuable reply!!

If you could suggest some good hole saw cutter for making cable entry holes in electrical panels, it would really help a lot. 

I have found CK hole cutters to be very satisfactory - they are available in 20 mm, 25 mm, and 32 mm.