How do you join parts together, and how do you choose between a permanent and a temporary joint?
Select and use appropriate methods to join and assemble materials, choosing between permanent and temporary fixings
A practical answer to the N(A)-Level D&T outcome on joining. Permanent and temporary joining methods for wood, metal and plastic, when to use each, and how the choice depends on strength and whether parts must come apart.
Reviewed by: AI editorial process; not yet individually human-reviewed
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What this dot point is asking
SEAB wants you to join and assemble materials using suitable methods, and to choose between a permanent joint that cannot be undone and a temporary joint that can. The key decision is whether the parts will ever need to come apart, because that, along with strength, decides which method to use.
The answer
Permanent versus temporary
The first question is always: do the parts need to come apart?
- A permanent joint cannot be undone without damaging the parts. It is strong and neat, used where parts never separate.
- A temporary joint can be undone and remade without damage. It is used where parts must come apart for repair, cleaning, or flat-pack transport.
Permanent joining methods
- Adhesives (glue). Bond a large surface; the type of glue must suit the material (wood glue for wood, plastic cement for acrylic, epoxy for many materials). Strong, neat, and permanent.
- Rivets. Join metal sheets permanently by deforming a soft pin through both pieces.
- Welding, brazing and soldering. Join metals by melting metal at the joint (mentioned for awareness; the strongest permanent metal joints).
- Shaped wood joints. Finger (comb) joints and similar increase the gluing area for stronger corners.
Temporary joining methods
- Screws. Pull parts together and can be removed; wood screws for wood, self-tapping screws for thin metal or plastic.
- Nuts and bolts. A strong, removable metal fixing for parts that must be undone.
- Knock-down (KD) fittings. Special fittings for flat-pack furniture the user assembles and can take apart.
- Clips and catches. Hold parts that open and close.
How to choose
Weigh two things: strength needed and whether parts separate. A fixed strong corner that never opens suits glue and a shaped joint; a shelf the user must flat-pack suits screws or KD fittings; a panel that opens for cleaning suits a clip. Always match the fixing to the material too.
Examples in context
Example 1. A flat-pack bookshelf. It must be sold flat and built by the user, so knock-down fittings and screws are used, letting the shelf be assembled and later taken apart without damage.
Example 2. A metal sign bracket. The two sheet-metal parts will never separate and need to be strong outdoors, so they are riveted, giving a permanent joint that resists weather and handling.
Try this
Q1. State whether each is permanent or temporary: glue, a nut and bolt, a rivet. [3 marks]
- Cue. Glue is permanent, a nut and bolt is temporary, a rivet is permanent.
Q2. A storage box lid must open and close many times. Suggest a suitable joining method for the lid. [1 mark]
- Cue. A temporary or movable fixing such as a hinge with screws, or a clip and catch.
Q3. Explain how you decide between a permanent and a temporary joint. [3 marks]
- Cue. Decide whether the parts ever need to come apart; if not, use a strong permanent joint, and if they must separate for repair, cleaning or transport, use a temporary one, matching both to the material and strength needed.
Exam-style practice questions
Practice questions written in the style of SEAB exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.
Original6 marksExplain the difference between a permanent joint and a temporary joint. Give one example of each and a situation where each would be the better choice.Show worked answer →
A permanent joint cannot be undone without damaging the parts. Example: a glued joint or a riveted joint. It is the better choice when the parts never need to come apart, such as the corners of a fixed wooden frame, because it is strong and neat.
A temporary joint can be undone and remade without damage. Example: a screw or a nut and bolt. It is the better choice when the parts must be taken apart for repair, cleaning or transport, such as a flat-pack shelf that the user assembles.
What markers reward: a permanent joint cannot be undone without damage (glue, rivet), a temporary joint can be undone and remade (screw, nut and bolt), each with an example and a sensible situation matched to whether the parts need to separate.
Original4 marksA wooden box must have strong corners that will never be taken apart. Recommend a suitable joining method and explain why it is suitable.Show worked answer →
A suitable method is a glued joint, ideally reinforced (for example a glued and pinned corner, or a comb or finger joint glued together). It is suitable because glue gives a strong, permanent bond over a large surface, the joint never needs to come apart, and a shaped joint such as a finger joint adds gluing area and strength while looking neat.
What markers reward: a permanent method (glue, possibly with a shaped joint or pins), justified by strength, permanence and a large gluing area, matched to the requirement that the corners stay together for good.
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