US Synthetic Bearings Site

PCD Insert (Nib) Sizes

Polycrystalline dies use an abrasion-resistant PCD insert (nib) at the core of each die. Typically the selection of the insert is based on the hole sizes for the die (new & recut sizes). More

Max hole size

Customers often ask about the largest hole size that is possible with a given PCD insert. The answer is that there are a number of important factors to consider regarding hole size.

Primary Factors:

Secondary Factors:

For most dies, the height of the insert is the limiting factor, rather than the diameter of the insert. The height is split into 4 main areas: entrance/bell, reduction, bearing, and exit/back relief. Typically the heights of the entrance, bearing and exit are defined and the reduction takes up the rest of the height of the PCD insert. The area of reduction and the reduction angle together define where the wire will make contact with the PCD. If this contact point is too high, flow of the lubricant can be choked off. If it is too low, the material is prone to center bursts. Ideally, the contact point would be near the center of the reduction. The figures below help illustrate this concept:

The largest hole size becomes a question of how much you are willing to compromise on contact point location. The following spreadsheet will help you work out the details on a given set of die specifications. The objective is to provide a tool that will generate a contact point and be used to select the proper PCD insert.

Contact Point Calculator

Calculate your contact point and find the best PCD insert for your application.
You can also download a spreadsheet version here

area of reduction

Reduction angle

Bearing Length


Entrance Height

Exit Height

Die Size(s)