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Specs & Details

Knock-Out boxes are manufactured to promote field flexibility for the contractor. The thin wall knock-out pan is non-reinforced to facilitate easy installation. However, each knock-out has been engineered to meet HS-20 loading so you can be sure it will hold up to the toughest job conditions. Knock-Out boxes can be provided with frame & grates or concrete lids to meet HS-20 or pedestrian loads.

Along with the following boxes, riser extensions are available to extend your box height to the desired finish grade.
Harper Precast maintains an inventory of standard “Knock-Out” catch basins in the following sizes. (W x L x H)

1'-0" x 1'-0" x 1'-0" *
1'-0" x 1'-0" x 1'-6" *
1'-0" x 1'-0" x 2'-0" *
2'-0" x 2'-0" x 2'-0"
2'-0" x 2'-0" x 3'-0"
2'-0" x 2'-0" x 4'-0"
2'-0" x 3'-0" x 3'-0"
2'-0" x 3'-0" x 4'-0"
3'-0" x 3'-0" x 3'-0"
3'-0" x 3'-0" x 4'-0"
4'-0" x 4'-0" x 4'-0"
* 1' x 1' Boxes Are Not Rated For HS-20 Loads
Features & Benefits
Lifetime Quality
Ultimate Durability
Long-Term Cost Efficiency
Variety of Choices
Concrete Boxes

Concrete knock-out boxes come in a variety of shapes and sizes depending on the intended use. They play an important role in the construction of a variety of large structures including underpasses, service tunnels, subways, outfalls, and bridges. They can also be used to build several different holding tanks and storage spaces. Because their ability to hold large amounts of weight is so critical, they must be made from the most durable materials possible. This is why you will most often find these boxes made from concrete that has been reinforced with a mesh knit material for extra strength.

The quality of workmanship used to fabricate concrete knock-out boxes is also an important factor that determines their strength. Enlisting the help of precast providers to build your project’s concrete boxes will generally yield the best results for a number of reasons. One important benefit that using the precast fabrication process can provide over onsite fabrication is quality control. Because pre-casting takes place off site, it can be done inside to avoid exposing the curing materials to the elements. Concrete that is mixed correctly and without interruption will cure to create the strong concrete knock-out boxes needed to build a solid structure. This also helps the fabrication process run more smoothly because work can be done regardless of the weather conditions. Pre-casting concrete boxes allows for a more freedom in design and a more economical and environmentally responsible fabrication process as well.

Finding a precast provider in your area who can supply the strong concrete boxes your structure needs will help you take care of an important detail of your project with as little stress and as much quality work as possible. Harper Precast has provided flexible and durable concrete knock-out boxes and other precast forms throughout Utah and the Intermountain West since 2006. We have built a strong reputation for quality workmanship and excellent customer service. Call or visit us online for more on our products and services.

Let us help you design your project today!
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