A plug and a patch address different parts of a puncture. The penetration through the tyre needs an appropriate filling, and the inner surface needs a suitable seal. A permanent workshop repair uses an approved system after the tyre has been removed and inspected; it is not equivalent to pushing a string into the hole from outside.
External plugs
An externally inserted plug may be sold as part of a temporary mobility kit. It does not provide the internal inspection needed to establish the tyre's condition. Do not treat it as a permanent repair or use it to bypass a garage's rejection of a damaged tyre.
If a temporary product has been used, follow its instructions and tell the fitter. The apparent disappearance of a leak does not establish that the tyre is structurally sound.
Internal patches
An internal patch seals the inner surface, but a patch alone does not necessarily address the penetration through the tyre. The complete repair must follow the applicable system and guidance. Product compatibility and correct preparation matter; this is not a choice to make from the appearance of the repair materials.
Combination and separate-component repairs
A combination repair unit joins the stem and patch functions. Appropriate separate filling and patch components can also form a recognised repair system. It is inaccurate to say that only a one-piece unit can ever be used.
The permitted injury area, size and condition requirements still apply regardless of which suitable system is used. A repair material does not make a sidewall injury or a damaged casing acceptable.
What a driver should ask
Ask whether the tyre will be removed and inspected, whether the proposed repair is permanent and what happens if internal damage is found. Explain any deflated running or previous temporary treatment. Confirm whether refitting and balancing are included in the price.
The useful distinction is a properly assessed, correctly performed permanent repair versus an unassessed temporary seal. Choosing the cheapest item called a plug or a patch does not answer that question.