Mac Tools sells replacement lenses for all their gauges based on lens diameter.

Glass lenses:

LENS-GLASS-1 - 2" gauge
LENS-GLASS-2 - 2 1/2" gauge LENS-GLASS-3 - 3 1/2" gauge
LENS-GLASS-4 - 3.66" gauge

Plastic lenses:

LENS-PLAST-1 - 2" gauge
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