Nominal Sizes
Every manufacturer uses nominal sizes. Nominal sizes are typically a whole number rounded up from the “actual” size. In sizing custom-size filters for exhaust frames, it is important to understand the difference.
EXAMPLE
18S: 18″x30′ Standard Accordion
Nominal height (or width): 18″
Actual height: 17.5625″
AFX: I can’t make an exact 18” or 20” without extreme waste. The base paper width for this size is 35.25 ” (39.25″ for 20″). Saw kerf is .125” or (35.25-.125)/2 = 17.5625. If I cut 18” from 35.25, I’d throw away the other 17.25” (double the cost).
All filters require +/- 0.125″ variance.
| NOMINAL | ACTUAL |
| 1M | 39.25″ |
| 36″ | 35.25″ |
| 20″ | 19.625″ |
| 18″ | 17.625″ |
| 24″ | 23.75″ |
| 29″ | 28.75″ |
Due to historical numbering, these sizes are “nominal” by sku (1MS, 36S, … 2972S). All other custom size skus are actual (+/- 0.125″ variance). If you require an “actual” size, send the inside dimensions of your frame. AFX will provide the appropriate size/part number.
Do you need a custom size?
Measure the inside of your exhaust frame for length and width (or height). Send us your actual inside dimensions and we will provide the manufacturer part number!