Office Chair Armrest Replacement

Was given the following chair https://www.officeworks.com.au/shop/officeworks/p/professional-ergonomic-extra-heavy-duty-mesh-chair-black-jbprofmbbk with a broken armrest padding.

Did a simple design to replace the armrest, the design has a flat top as it is meant to have foam and fabric to go over it.

The screw holes are sized for M5 heatset insert.