This is the v2 hybrid insulator I've been testing - sliced and diced for your viewing pleasure. For a solid PEEK insulator it would be necessary to turn down the heater barrel a few threads in order to establish a tight seal. I've tried PTFE both ways (with the barrel turned  - yellow background and with a fully threaded barrel, below). Using a turned barrel with PTFE leaves a slight gap along the top edge of barrel. I don't know if this makes a significant difference but PTFE is soft and easily distorted. The objective is to box-in the PTFE so that it provides a low-friction channel for PLA but can't distort.  [The scruff along the threads is from the band saw.]

The following photo of the v1 hybrid (yellow background) shows the damage inflicted during one of the v1 PLA stress tests. First, ABS was extruded at 220C. Then the barrel was allowed to cool and then re-heated to 170C. With the barrel full of softened but unmelted ABS, PLA filament was then forced in. 170C is at the low end for extruding PLA and too low to extrude ABS - though the ABS softened and extruded very slowly. This scenario created a brutal environment where the PLA filament did not strip because the PLA was able to keep moving though very slowly (since the ABS was slowly extruding). This produced substantial pressure within the hot-end and the weakest link was the PTFE / heater barrel seal. The PLA being forced in needed somewhere to go and since the only place to go was up, it stretched the PTFE. Hence the addition of the PEEK plug above the PTFE insert in v2. [The gap/damage between the base of the PTFE insert and PEEK housing was unrelated and occurred while attempting to remove the heater barrel before slicing it on the band saw.]

The Parts that make up a v2

Almost assembled

Finished

Now, add your HeatCore, nozzle, thermistor and insulation. Heat. Print :)

Note: If you are just printing with ABS then you don't need a hybrid insulator - a solid PEEK insulator work great! The hybrids are just needed (at least they are currently needed) when you are using PLA or PLA and ABS.