There are many applications where a machine thread is required in both wood and in sheet metal which is too thin to hold a tapped thread well. Threaded inserts are very useful because any assembly put together with them can be dismantled. They are therefore perfect for prototypes, jigs and permanent assemblies which are more rarely broken down but which require this feature as a part of the design brief.
Inserts for wood
Our threaded brass and zinc alloy inserts have an external thread which is suited to wood. These inserts have an external thread with knife edges which bite deeply into the wood and keep the insert securely in place. The internal thread is a metric or imperial standard machine thread which allows numerous fasteners to be used.
Brass inserts, although supplied with a screwdriver slot, are best set in place by using a fastener of the correct size as a mandrel - either a bolt or machine screw. See the suggested mandrel assembly below. Note that a backing nut and washer can help with routine removal of the mandrel. To work around the tendency for the insert to wind back out after seating use two nuts tightened against each other with some spare thread either side to allow the nuts to be parted and the mandrel withdrawn (this mandrell variation not illustrated). You will typically, although not always, take care to keep the insertion process at right angles to the wood. You can use a drill press for this process to improve the accuracy of the insertion. Note that the design of the insert assists with accurate insertion.
Although the screwdriver slot in the brass inserts can be used for insertion, the insert may more easily be damaged with this method. The insertion hole size may need to be fractionally varied for some extremely hard woods and a dab of glue on the external thread of the insert offers further permanancy.
This is the suggested rig for setting both brass and zinc alloy inserts. Be sure the washer is used in reverse, polished side against the insert. A dab of oil on the insert can also ease release of the mandrell.
Zinc Alloy Inserts
These can be set using an allen key although an identical procedure to the one suggested above for brass inserts works best because the vertical alignment is easier to eyeball when setting.
Dimensions and drill selection:
Inserts for metal
Our inserts for metal sheet require a setting tool. See Item Code: T8358. This British made setting tool is supplied in a kit with a selection of metric 4, 5, 6 and 8mm thread inserts. Click HERE for additional inserts.
The application is identical to using a pop riveting tool and can be carried out entirely from one side of the work
Drill an appropriate diameter hole (note the tolerance here is quite tight, you must source a correct size drill), insert the correct mandrell for the insert in the pliers (take care, some of the parts have a left hand thread), wind on the insert and set the insert as you would a pop rivet taking care not to over tighten the setting tool.
Unified Thread System
The UNC standard uses gauge numbers for sizes under 1/4 inch which causes some confusion.
It is not immediately clear that an #4-40 UNC designated screw will be a close enough fit for what Australians would know as 1/8 inch Whitworth.