want to install a glass insert in a steel exterior door the house is brick & the door is not standard size Answered

How big is the insert you are planning ?

question: are most steel doors insulated & would you know what type of material it is? the reason i'm asking is if i screw up the door i may have to enlarge the opening that maybe more than i want to deal. i appreciate your thoughts

Mask the door carefully: I think I would make a stencil in a piece of plywood to cut through - if the cutter jumps, it won't ruin the door.

Cut it with a thin blade cutting disk in an angle grinder. The edge will need reinforcing. You could get away with screwing wood inside the edges, a glass insert can then be glued in place, and a trim applied by screwing into the edge bracing.

Steve