Some bulldog-type extruders have too much free space between their body and the gearwheel. It means that filament can simply bend, then clog and finally get shredded by the gear (it happened to me next day after mounting bulldog in my printer). This little upgrade guarantees that such situation will never happen again.
Inspired by original design published by Michael Foegelle on grabcad.com I've decided to measure the extruder and prepare my own version of this guide.
Devil Design PETG
Little sanding job might be required to get perfect fit in your extruder. The part should fit tight.