Threaded inserts are one of those items that you are using every day, without knowing it. They are part of so many every day items, like chairs, tables, toilet seats, plug sockets, cars, planes and many more. Threaded inserts are usually brass, steel or stainless steel and are used in plastic castings, housing and parts to create a metal thread to allow screws to be used in the products listed above.
Threaded inserts are often used to repair a stripped threaded hole, to provided a durable threaded hole in a soft material, to place a thread on a material too thin to accept it, to mould or cast threads into a work piece therefore to eliminate a machining operation, or to simplify changeover from unified to metric threads or vice-versa.
Threaded inserts are available in a variety of shapes, which are determined by their use and function. The cylindrical metal shapes, which are placed in holes to provide threaded tracks for bolts and screws, provide extra durability, strength and stability.
What size hold should be used for threaded inserts?
As each threaded insert is different, and each screw or bolt that is being inserted into it also differs depending on size and material, each hole will change in size too. Fitsco threaded inserts all come with a recommended hole size, which is what we advise to ensure that our threaded inserts perform to the highest standard.
Choosing the Best Threaded Insert
Choosing the best threaded insert is an essential part of your project, and finding out which one is best is determined by a number of factors, and we run through those here.
What type of material is the threaded insert going into?
The material (thermoplastic, thermoset or DMC etc) in which the insert will be installed will directly influence the correct choice of threaded insert, the achievable performance and installation method.
What ‘torque’, ‘pull-out’ and ‘jack-out’ performance is required?
Torque is the maximum rotating force (Nm) that can be applied to the insert before it ‘spins’ in the moulding. Pull-out is the maximum force (Kg), applied in a direct line, that results in the insert being pulled out of the moulding. Jack-out is the maximum rotating force (Nm) that can be applied to the threaded inserts before it starts to be pulled-out of the moulding and occurs when the design of the two mating parts has not been done correctly.
Do the threaded inserts need to be ‘headed’ or ‘unheaded’?
The majority of threaded inserts that we design, make, manufacture and supply are unheaded as they are usually installed flush into a blind hole. The headed style are used in a through-hole application to prevent them pulling through. They can also be used in applications where there is an oversize clearance hole in the mating part preventing a jack-out situation and for use as an electrical contact.
How to choose the appropriate brand of threaded inserts?
Fitsco offer several different types of threaded inserts to suit all types of applications, materials and performance.
How do you fit threaded inserts?
We are often asked by customers how they should insert their threaded inserts. When screws or bolts are threaded directly into plastic, wood, metal or fibreglass components, failures often occur. Threaded inserts provide stability, strength and durability to the joint. There are several methods of installing threaded inserts, including thermal and ultrasonic, as well as being pressed, moulded and screwed in.
What’s the best way to install threaded inserts?
There are two methods of installing threaded inserts; post-moulded and moulded-in. The three main methods of installing post-moulded threaded inserts are using heat or by ultrasonics by cold or screw-in, with each method having its own advantages and disadvantages. The easiest method of installation is to press the threaded inserts in cold. You will get a better performance if the inserts are put in hot, using some type of installation machine. The screw-in range of inserts has to be installed with specialist equipment and is therefore the hardest to method of installation, but provides the best performance. Moulded-in installation is the method that provides the maximum performance, but has the disadvantage of requiring the threaded insert to be installed directly into the mould tool. This method is mainly used in thermoset or DMC mouldings where cycle times are slower, so the time taken to install the threaded inserts is not too much of a disadvantage. The majority of inserts blind, which stops plastic material going inside the insert and contaminating the thread.
How do you install threaded inserts in composite or fibreglass?
The standard method for thick or cored composite is to epoxy a knurled threaded insert into a small hole. Another method is to tap the hole in the composite and install a self-tapping threaded insert, covering both hole and threaded insert with epoxy. With both types, the insert should be mounted on a greased screw to protect the internal threads from the epoxy. An insert that is bonded will be durable and stronger than a sheet-metal screw inserted straight into the fibreglass, but it is not an effective replacement for a thru-bolt with a backing plate.
How do you install and use threaded inserts in metal?
If a threaded insert is being installed in metal, most will require tapping the hole, although there are some types of self-tapping threaded inserts that can be used in soft metals. The taps are usually a special size and thread intended just for the particular insert, which will typically come with the insert as a kit. Coil threaded inserts may also require an insertion tool to tighten the coil
How do you install and use threaded inserts in wood?
Threaded inserts which are being installed into wood can be barbed, which are usually pressed or hammered into the hole. Screw threaded inserts will prove to be more durable, however. These are typically inserted by spinning, like a wood screw. Some will have a hex socket and are installed with the use of an Allen wrench. Slotted inserts could be installed with a screwdriver, but due to the slot being fragile, the most preferred method is to thread a nut, then the insert, onto a long bolt. The nut should be locked against the insert, then the threaded insert should be turned into the hole with a wrench or socket.
Why use threaded inserts in wood?
Threaded inserts will provide strengthening, durability and stability to your products.
How do you install threaded inserts in plastic?
Threaded inserts are typically pressed into plastic with the assistance of heat. A more unorthodox method would be to thread the insert onto a bolt. Use pliers to hold the bolt with the insert in place of the hole, whilst applying pressure downwards. The bolt should be heated with a soldering iron, and as the heat transfers to the insert, which after a minute or so, should begin to sink into the softening plastic. Downward pressure should be continued until the threaded insert is at the sought depth, at which point the heat should be removed and hold the bolt steady until the plastic has stiffened.
Blog by Dan - 13th June 2019