ATB M3000C step box C-frame mounting kit hardware with bolts, spacers, nuts and rubber strip

ATB M3000C Step Box C-Frame Mounting Kit, Steel Bolt-On

$23.25
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Features

  • Bolt-On C-Frame Kit: The M3000C bolts an ATB SB step box to a C-frame truck through the back of the box, using the box's internal mounting brackets.
  • Primer and Powder Coat: The steel parts carry a zinc epoxy primer under a baked MR powder topcoat.
  • Grade 8 Bolts: Four 1/2" x 2" Grade 8 bolts with 1/2" flat washers and lock nuts hold the box to the frame.
  • Rubber Strips: Two 3" x 12" rubber strips go between the box and the frame.
  • Load Rating: ATB's product page lists the kit for step box and steps installs up to 300 lbs.; its 2026 catalog and install sheet rate it at 150 lbs. max of cargo, and above that ATB points to its M2000 or M2100 L-brackets.

Description & Fitment

The ATB M3000C is the bolt-on kit for mounting an ATB SB step box and steps to a C-frame truck. Four 1/2" x 2" Grade 8 bolts pass through the back of the box and the frame rail, with rubber strips between box and frame. The steel parts carry a zinc epoxy primer and a baked powder topcoat.

Fitment & Compatibility

How to choose: the M3000C bolts through the frame web and needs four 9/16" holes in the frame. If you would rather not drill the frame, ATB's M3000H and M3001H hook kits hang the box instead.

For more than 150 lbs. of cargo, ATB recommends its M2000 or M2100 L-brackets.

Fits: ATB SB step boxes on C-frame trucks (bolt-through mount)

About ATB

ATB

American Truckboxes (ATB) builds aluminum and steel truck boxes, tanks and storage in Blanchard, North Dakota, and has done so for more than 25 years, by its own account. Its range covers pickup crossover, side-mount, chest and drawer boxes, service-truck boxes and packs, fuel tanks, and heavy-truck and trailer boxes.

Authorized ATB dealer. Prestige Truck is an authorized ATB dealer: every box on this page is built by ATB to the part number shown.

Frequently Asked Questions

Will it fit my truck?

It is made for ATB SB step boxes on C-frame trucks. Check that the frame web has room for the four bolts and is clear of existing brackets.

Do I have to drill?

Yes. The step box is not predrilled because frame hole patterns vary: you drill four 9/16" holes in the back of the box and four 9/16" holes in the frame, following the truck maker's frame-drilling guidance.

What if I carry more than 150 lbs. in the box?

ATB's install sheet says the box needs no outside brackets up to 150 lbs. of cargo; above that it recommends ATB M2000 or M2100 L-shape mounting brackets.

Which bolts does it use?

The install sheet lists four 1/2" x 2" Grade 8 bolts. ATB's product page also lists frame-mount bolt options of 1-1/2" and 2.0".

How does it ship?

By freight from the ATB factory in Blanchard, ND, with lift-gate delivery available. For Alaska, Hawaii or Canada, contact us for a freight quote before you order.

What should I check when it arrives?

Check it before the driver leaves: look it over for dents, scratches or shipping damage, note any damage on the delivery receipt and send us photos.

Installation

Install time About 1.5 hours
What's involvedYou drill four 9/16" holes in the back of the step box and four in the truck frame, then bolt through with rubber strips between.
Tools
  • 3/4" ratchet wrench
  • 3/4" wrench
  • Tape measure
  • Drill with 9/16" or 11/16" bit
  • Utility knife
  • Blocks

Here's the short version. Follow ATB's install sheet (below) for your truck's exact positions and hardware.

  1. Check all parts against the parts list and make sure there is room to mount the box.
  2. Set the step box on the frame to confirm it fits there. The box is not predrilled because frame hole patterns vary.
  3. Remove the box and drill four 9/16" holes in the back of the box, laid out as on ATB's M3000C drawing.
  4. Put the box back, mark the holes onto the frame, then remove the box and drill four 9/16" holes in the frame (follow the truck maker's frame-drilling guidance).
  5. Apply the 3" rubber strip to the box, cut the bolt holes in it with a utility knife and set the box back on the frame.
  6. Insert the bolts with washers, put a flat washer under each lock nut and tighten all nuts securely.

Stuck on a step? Ask our install experts

What's included
  • Four 1/2" x 2" Grade 8 bolts
  • Four 1/2" flat washers
  • Four 1/2" lock nuts
  • Two 3" x 12" rubber strips

Specifications

BrandATB
Part NumberM3000C
TypeStep box C-frame mounting kit
MaterialSteel
FinishZinc epoxy primer, black MR powder topcoat
Bolt size1/2"
Weight2 lbs.
Made inUSA

Warranty, shipping & returns

  • Warranty

    ATB covers its standard truck boxes with a 60-month (5-year) limited warranty for the original purchaser; it is not transferable.
    • For a warranty claim, contact us with your order number and photos and we will work it through with ATB.

  • Shipping

    Ships by freight from the ATB factory in Blanchard, ND; lift-gate delivery available.
    • Alaska, Hawaii and Canada: contact us for a freight quote before you order.
    • We email your tracking details as soon as it ships.

  • Inspect on delivery

    Check the box when the freight arrives, before the driver leaves: look over the lids, doors, corners and welds for dents, scratches or shipping damage. Note any damage on the delivery receipt and send us photos. Check it as soon as it arrives.
    • Look for crushed ends, punctures or tears in the carton.
    • If something looks wrong, take photos of the box and the parts (and if a driver asks you to sign, note the damage on the receipt).
    • Open the box and check the parts against the parts list before you install.
    • Email support@prestigetruck.com right away with your order number, a short note and photos. We send a replacement or a full refund at no cost to you.

  • 30-day returns

    Return it within 30 days of delivery, unused, in the original packaging, with proof of purchase.
    • Email support@prestigetruck.com with your order number. We reply within 1-2 business days with instructions.
    • Damaged, defective or wrong item: we send a prepaid label or arrange a pickup.
    • Changed your mind: you pay return shipping. No restocking fee.
    • Refunds go back to your original payment method within 7 business days of approval. See our returns policy.
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