The Tapepro Corner Box and Compound Tubes can be fitted with a number of applicator heads, including the Cornice Heads and the Manta-Ray.
In addition we also have applicator heads for 90 deg internal and external corners, and flats.
Internal – AH-38, Applicator Head 38
For dispensing ribbons of joint compound to both sides and apex of internal angle joints, horizontal or vertical, prior to applying paper tape or internal beads by hand. Also for applying addition compound to internal joints for top coat finishing withStraight Glazers.
External – OAH, Outside Applicator Head
Perfect for mudding external angles prior to fitting Trim-Tex Mud Set Bead. This a great and extremely fast way to fit your corner beads!
Like the AH-38, the OAH is designed to apply joint compound to the apex, making for the strongest joint possible.
Flat – FTA, Flat Tear-away Applicator
Designed specifically for use with Trim-Tex Mud Set Flat Tear-away bead.
This is a very quick and easy way to install bead and creates less mess.
Description taken from http://tapepro.com/tools/mud-heads/