Copper Fitting 7/8 to 1/4 (HVAC Dimensions) Reducer / Increaser Copper Coupling & HVAC – 3/4 to 1/8 (Plumbing Inner Dimensions) 99.9% Pure Copper - 5 Pack Brown Ideal for Walls & Ceilings:

Ideal for Walls & Ceilings: Designed for seamless installation in standard 18" X 4" duct openings

Actual Filter Size – 21 3/4"w x 11 3/4" x 1"

Actual Filter Size – 29 3/4"w x 33 3/4" x 1"

actual front end outer dimensions are approximately 26

+ Product Details Size - 20"w X 22"h is the size for the duct opening measurement only

Copper Fitting 7/8 to 1/4 (HVAC Dimensions) Reducer / Increaser Copper Coupling & HVAC – 3/4 to 1/8 (Plumbing Inner Dimensions) 99.9% Pure Copper - 5 Pack Brown Ideal for Walls & Ceilings:How to measure HVAC & Refrigeration tubing Refrigeration tubing is measured by it's outside diameter O. D: 1 4, 1 2, 5 8, 3 4, 7 8, 1 1 8, 1 3 8, 1 5 8, etc. Plumbing tubing is measured by it's inside diameter I. D: 1 8, 1 4, , 1 4, 1, 1 1 4, 1 1 2, 1 3 4,etc. Rule of Thumb: "HVAC" nominal tube sizing 1 8; larger than the same nominal size "plumbing" pipe. So for example, a 1 4" HVAC fitting, is the same as a 1 8" Plumbing1fitting. Or a 1 2" HVAC