Mold corner balance plates and parallel blocks, made to your drawing. The ground spacers that set and hold plate separation — usually four of them, one at each corner, and their job is to be identical. Send a drawing, the required height and tolerance, or the existing set photographed with a caliper, and we quote in writing, normally within one business day.

The spec that matters is not the height — it is the height match

A parallel block set is a matched set. What the mold cares about is that all four are the same, to a much tighter band than any one of them needs to be to its nominal.

If one corner is 0.02 mm taller than the other three, the plate above it does not sit flat: it rocks on that corner, and the clamp force closes the gap by flexing the plate. What you see afterwards is flash at one corner, a witness line that moves as the mold heats, or bolts that keep loosening on the same side.

So when you order, give us two figures: the nominal height with its tolerance, and the height match required across the set. These are different numbers, and the second is usually the tighter one. If you only give a nominal, we quote to normal practice and state on the quotation what match we will hold — check that figure against what your mold needs.

Parallelism, and why it compounds

Each block also has to be parallel top to bottom. A block that is in tolerance on height but tapered across its face tilts the plate in a second direction, and the tilts from four corners add up in ways that are hard to diagnose from the moulded part. Parallelism and flatness on the bearing faces are worth calling out explicitly.

Bearing area and surface condition

• Do not undersize the footprint. These carry clamp force in compression. A block with too little bearing area indents its mating plate over time, and once the plate is indented the height match is gone regardless of how good the blocks were.
• Fastener heads must sit below the bearing face. A counterbore that is a hair too shallow makes the screw head the load-bearing point. This is a common and entirely avoidable failure — mark the counterbore depth if there is any doubt.
• Ground faces, deburred edges. A raised burr at an edge does the same thing as a proud screw head.

What to send us

• Length, width and height, and how many blocks in the set
• Height tolerance, and the required height match across the set
• Flatness and parallelism on the bearing faces
• Hole, counterbore and centre-distance layout, with counterbore depth
• Whether the part is flat, stepped, angled or tapered
• Material and hardness preference, or describe the clamp force and we will propose one
• Quantity, destination and required date

Replacing a set on a mold that flashes at one corner? Measure all four of the old ones and send us the numbers — if they differ, you have found your problem, and it is worth knowing that before new parts are made.

Documentation and confidentiality

Material certificates, hardness results and dimensional inspection reports are available on request, with scope and any cost confirmed in the quotation. Technical files are used to evaluate and fulfill your inquiry or order. They may be shared only with relevant manufacturing, inspection, logistics or service partners as needed. Send only files you are authorized to share. See our Privacy Policy. NDA on request from rfq@privleymold.com.