MacLean Highline Develops Unique MPT Fastener Insert for Underground Enclosures

The Challenge

Traditional handhole enclosures have covers at grade level that have retaining bolts that are threaded into the box. All legacy Highline boxes were fitted with hardware placed into the box at the time of assembly. This new approach places the insert and hardware in the box at the time of manufacturing thus reducing the time required to assemble orders. The old cavity tooling was specific to the nut size and susceptible to damage or loss during the casting process. Also, the tooling was cast into each part then had to be removed from the part and replaced in the mold.

There Must Be a Better Way!

We asked ourselves, “How might we do this differently?” Team members were assembled from Production, Assembly, and Engineering. Starting with a blank sheet of paper and building off each other’s ideas, we developed the MPT insert. It consists of a hollow injection molded piece that is cast into the part permanently. At the time of casting, the MPT contains the nut and other required hardware.

After several iterations, a design that could hold all our inserts was developed. We requested samples from the York facility in South Carolina. They sent us thirty 3D printed parts that were cast into boxes and put to the test requirements of ANSI/SCTE 77 for torque and pullout. After some additional refinements, the design was ready for production tooling. After receiving the first parts, additional testing was performed to confirm that the production parts performed as well or better than the prototypes. These proved to be as good or better, so the next step was to order the material and get the inserts into production. All the legacy box molds require some level of modification to be able to accept the insert while all new tooling is setup for the MPT Insert.

Casters Say…

They like the MPT inserts because they do not have to be prepared or cleaned like the previous tooling pieces. The MPTs are more stable in the mold and remain in position better than the old tooling. The MPTs do not get removed from the part and tooling doesn’t get lost or damaged.

Assembly Department Benefits

Having the hardware already installed in the box greatly streamlines the assembly process. The MPT is preferred since the cavity is universal and not restricted to one size of nut. This type of flexibility allows casting of the part with certain size and style of nut.

Customer Benefits

Customers have the same benefits that they have required in the past having an insert that is floating and replaceable. They also have the flexibility to make a size change in the field going from a standard thread to a coil thread without changing the box.

Favorable Impacts

The MPT impact will be felt in production efficiencies due to the set-and-forget insert placement in the mold, in assembly due to the pre-installed hardware, in our yard since the insert size can be changed, and in our machine shop which produced the old-style metal tooling. The MPT initiative is a strong team effort and shows what can be accomplished when dedicated people strive together for improvement.


MPT inserts holding three different nut sizes


MPT inserts with doors closed, ready to be installed in the mold


Side Views


MPT insert cast in a box


MPT in box with door closed