<p>Prosthetic devices are often framed as biomedical solutions designed by professionals to restore function to disabled bodies. Drawing on ethnographic research conducted with amputees in France, the Netherlands, and Germany, this article challenges this view by examining how prosthetic users actively modify, fabricate, and reconfigure their devices in everyday life. These practices, we argue, are forms of prosthetic tinkering, that is, situated interventions through which users adjust, repurpose, or create prosthetic devices and arrangements in response to bodily sensations, environmental constraints, and social interactions. Through ethnographic cases, such as socket adjustments, homemade task-specific prostheses, alternative mobility arrangements, and aesthetic modifications, we show that these practices constitute a form of disability expertise grounded in experiential knowledge of bodies and technologies. This article shows that prosthetic tinkering allows amputees not only to improve comfort and functionality, but also to navigate ableist norms, manage the visibility of disability, and reshape social relationships. Importantly, prosthetic tinkering mainly takes place in the domestic sphere, i.e., in kitchens, garages, and living rooms, rather than in the more visible or publicised sites of technological innovation such as laboratories, engineering workshops, or fablabs. By foregrounding these often-overlooked practices, the article contributes to science and technology studies and critical disability studies debates on agency, expertise, and the politics of design, highlighting prosthetic modification as a situated practice of world-making rather than a mere technical adjustment.</p>