21x27x1 (20.63x26.25x.75) MERV 8 Aftermarket Trane Replacement Filter (2 Pack) Replacement pleated air filter for Trane. Nominal size 21 x 27 x 1. Actual size 20 5/8 x 26 1/4 x 3/4. Can be used to replace washable pre-filter #BAYFTFR21W1A. This is an aftermarket filter.