The part that the collet holder slips into is shown above. It is also tool steel. This piece fits into the slot that would otherwise be used to hold a square toolbit (0.375) There are two 1/4-20 threaded brass fasteners, with knurled aluminum knobs, to secure the collet holder.
This photo must be updated, when I get a 1/2" ER20 collet. This collet holder & collet is a 180 DA. I want to use the ER20 holder because it is longer, and has a much smaller locking nut. That is needed to be able to position an internal threading tool for sharpening. The brass ring can be used to prevent excess movement of the collet holder.
On the left is the assembly utilizing the collet holder. It should be noted that the tool holder can be positioned on either side of the vertical piece, depending on clearance and geometry requirements.
