Hole configuration, hole diameter, and hole depth can have a significant impact on threaded insert performance and installation. Recommended hole configuration and dimensions are included with the insert specifications which follow. However, there are some useful general guidelines to follow. Groov-Pin recommends one of three hole configurations depending upon insert type:

• For softer metals and brittle plastics, a straight hole with up to 1 degree taper and counterbore or countersink
  (fig. 8a).
• For plastics, a straight hole with taper up to 3 degrees and no counterbore or countersink (fig. 8b).
• For plastics, a hole with a taper of 8 degrees and no counterbore or countersink (fig. 8c).

Recommended hole diameters are included with the insert specifications which follow. Counterbore dimensions are included where appropriate. Note that actual hole dimensions are specified and not core-pin or drill sizes.

When evaluating insert performance, hole diameter may be adjusted to optimize threaded insert installation and performance. Although the inserts are designed to operate over a range of hole sizes, smaller hole sizes yield higher pull-out resistance in softer materials and larger hole sizes provide easier installation in more brittle or higher-tensile-strength materials.

When considering bosses in a plastic part, stepped holes may be specified to minimize undesirable sink marks (see fig. 7). Limit the maximum diameter of the stepped hole to 80% of the diameter of a straight hole (fig. 8a,b) or to the minor diameter of a tapered hole (fig. 8c).

8a Straight Hole with Counterbore

Straight hole with taper up to 1 degree of diameter H and minimum depth 1.2 times insert length L. Counterbore of diameter equal to insert diameter D and depth C. Alternatively, a countersink of diameter D with 60 deg. included angle may be specified for metals. Minimum wall thickness W.

8b Straight Hole with no Counterbore

Straight hole with taper up to 3 degrees of diameter H and minimum depth 1.2 times insert length L. Minimum wall thickness W. No counterbore or countersink.

8c Tapered Hole

Tapered hole with 8 degrees taper of major diameter H1 and minor diameter H2 with minimum depth L2 equal to insert length L plus 0.030 inch.

Hole depth for blind holes should be at least the depth of the threaded insert plus two pitches of the internal thread (see fig. 5c on Designing with Threaded Inserts main page). This will allow full engagement of the mating fastener and avoid fouling of the internal thread by base material during installation. A hole depth of 1.2 times the insert length is recommended. For through holes, the material thickness should be greater than the length of the threaded insert.


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