Bolt Boxes — Holding Down Bolt Clusters Made to Your Drawings

A bolt box — also called a holding down bolt cluster — is a group of holding down bolts fixed into a template at the exact spacing and projection set by your structural engineer, ready to cast straight into a concrete foundation. It's what gives BoltBox its name, and it's the product our groundworks and civil engineering customers rely on to keep their site programme moving.

Every bolt box is made to order from your drawings. We don't get involved in the structural calculations — your engineer specifies the details and we build precisely to them.

Built to your engineer's specification

Each bolt box is set out from the dimensions on your foundation drawing. The variables that change on every job are:

• Bolt diameter (M16 to M36)
• Bolt length
• Bolt hole centres (the spacing of the cluster)
• Plate width and thickness
• Bolt embedment (depth set into the concrete)
• Bolt projection (length standing proud for the stanchion)

Grade and finish are also specified, though in practice almost every cluster is Grade 8.8 high-tensile, self-colour — roughly nine in ten are self-colour, with galvanised available when required.

Sizes and configurations

We make bolt boxes from M16 up to M36. The most popular is M20, closely followed by M24, and the most common arrangement is a 4-bolt cluster — 2, 6 and 8-bolt clusters are made to order too whenever the design calls for them.

What's in a bolt box

Each made-up cluster is supplied complete with:

• Holding down bolts (Grade 8.8, made to British Standard)
• Nuts
• Square plate washers
• Tapered waxed cones
• A plywood template that holds everything at the correct centres

Need the parts on their own? Every component in a bolt box is also available to buy individually:

How a bolt box works on site

The bolt box is cast into the foundation with the plywood template left in place during the pour. The day after, the template is stripped so the waxed cones can be removed and each bolt given a slight movement to confirm it's free, then refitted to keep debris out of the cone voids. It's removed for the final time just before the steel erectors set the stanchion in place — leaving clean, accurately positioned bolts every time.

Why pre-made bolt boxes keep your job moving

Buying loose bolts and setting them out by hand on site is slow and risks costly errors. Have us make your bolt boxes up before you start on site and your programme flows:

Accurate centres, the right projection and embedment, and no time lost — that's the difference a pre-made cluster makes.

Two ways to order

Either way, send us your drawing and we'll quote it.

Fast lead times

Most bolt boxes are turned around within a week — often just a couple of days. When a job's urgent, we'll do everything we can: we've built and handed over clusters the same day for a contractor who was stuck.

Bolt boxes — frequently asked questions

What is a bolt box?

A bolt box is a group of holding down bolts fixed into a plywood template at the spacing and projection specified by your structural engineer, ready to cast into a concrete foundation. It's also known as a holding down bolt cluster.

What sizes of bolt box do you make?

We make bolt boxes from M16 to M36. M20 and M24 are the most popular, most commonly in a 4-bolt cluster, with 2, 6 and 8-bolt clusters made to order.

What do I need to provide to get a bolt box made?

Your structural engineer's foundation drawing, which specifies bolt diameter, length, hole centres, plate size, embedment and projection. We build precisely to those figures.

What's the lead time on a bolt box?

Usually within a week, often a couple of days. We'll always try to help when a job is urgent.

Can I supply my own bolts?

Yes. Many regular civils customers supply the bolts and we make the templates and build the clusters. Or we can supply everything complete — just ask for a quote.