Many brands of shoe have cleat mounting positions that are too far forward for many riders. Mavic, Vittoria, Carnac and Pearl Izumi are examples, though a lot depends on individual foot proportions and how the foot fills the shoe.
For those wishing to attempt a ‘home handyman’ approach to modifying their cleat position, threaded eyelets are necessary. Supplied in sets of eight (two spares if you make a mistake). Included are instruction sheet, longer than standard cleat mounting bolts (often necessary), and a long M5 bolt to help seat the eyelets.
This job should be within the capability of anyone who knows their way around tools and has a handyman mentality. However, before proceeding further, first and foremost you need to understand that any modification of a cycling shoe carries a potential risk to the user of the modified shoes. If you are not willing to take personal responsibility for this risk, do not purchase this product.