Door and architrave fitting spacer

Im a carpenter by trade and a colleague wanted a spacer bloack to quickly mark the side of a door frame before installing architrave while also being able to space the door to the head of the frame correctly. the block has a 8mm lip on 2 sides so you can put into the corner of the head marking the head of the frame and the leg at the same time moving down and across to mark multiple locations ready to fit architrave. This lip is also 2.5mm thick allowing the 2.5-3mm desired gap between door and frame when positioning door to mark frame. 

after often using a 3mm spacer he found the gap to always be closer to 3.5 or bigger getting close to the 4mm limit on regulations hence the 2.5mm lip.

Still new to designing so would love photos of your prints and appreciate any comments.

Thanks and happy printing.