Unlike Fender replacement guitar parts, Squier upgrades are not entirely easy to source. 

Here are a few considerations to help in your search. 

Specification 

Fender USA and Made in Mexico guitars are well catered for. Their parts are a US specification, and variation between models is often a difference of a modern or vintage style part. 

It is completely different for Squier upgrades. 

Although they are considered a metric spec, their parts vary heavily between models and are not always what would be considered “standard”. This is made even more difficult by the variance in things like body and headstock thickness. The Squier Bullet Strat, for example, has a thinner body than a standard Strat. 

To source the best upgrades, that will be a direct fit, you will need to accurately measure the part you are replacing. For machine heads, this would be the headstock hole and screw spacing; the tremolo would require post spacing, the string spacing, and the depth of the body; replacing pots would require knowing the thread diameter. 

Upgrading to Imperial 

Given how much easier it is to source US specified parts, and the consensus that they are better quality components, you might want to consider fitting them instead. 

Imperial spec parts are usually slightly bigger and will need adjustments to fit. You could do this yourself, with the use of some tools, or you might want to consider the services of a guitar technician to install the parts. 

Budget 

Squier guitars are budget-friendly, so it is important to consider the cost of any upgrades you choose. Any upgrade of a value more than the guitar would not add much value to the resale price, and you would be better off upgrading the guitar to top-end Squier guitar or a second-hand MIM. And do factor in the cost of guitar tech, if you do go down the route of imperial parts.

The Outcome 

Ultimately, choosing the right Squier upgrades comes down to this: what do you want to achieve? Better tuning stability? Improved playability? Different tone? And will the upgrade make a difference?

Being a budget guitar – though by no means a poor-quality instrument – expectations must be tempered with the installation of any upgrade part.