This is a system of parts refereed to as a Luer locking taper.  This is standard that enables the user to twist on different applicator tips for different needs.

The circle A in the image is actually two parts.  The black cap is the luer lock itself. and the orange part is a cap.  The cap is used to prefill the bottle and seal in its contents till it is ready to be used and prevent it from leaking out.

The circle B is refereed to as a tapered tip.   This green tips is an 18 gauge tapered tip.  The tapered tips are good for adhesives because the taper helps prevent adhesives from hardening in the tip and clogging the tip.  It also helps deliver a smooth flow of adhesive.  Another advantage of the system is when a tip is clogged you can twist it off and twist on a new clean tip.  Since luer lock tips are a standard you can get many different types.  The tapered tips typically area available in 12-34 gauge and there is a color coding standard so you can tell the gauge by the color of the tip.

The circle C: is the tip sheath.  The advantage of this is you can store the tip on the bottle with the sheath and outer cap and it will help prevent the adhesive from filling the cap with adhesive if it tips over.  The size match between the tip and the sheath is key to getting it to work as designed