Open source hardware has developed rapidly since the last 2 decades, thanks to access to Internet and availability of novel interactive manufacturing technologies (for example 3D printing or collaborative platforms). Several researchers worked on how to characterize OSH. Bonvoisin and Mies (Procedia CIRP 78:388–393, 2018) defined the “open-o-meter”, i.e. a series of criteria to measure the openness of an OSH project. These criteria fall into two categories: product openness and process openness. The open-o-meter gives clear guidelines on measuring product openness by verifying access to specific types of documents, however the criteria to measure process openness are relatively implicit. In this paper, we propose to measure an OSH project’s process openness by identifying different types of collaboration tools in that project. We will evaluate 226 OSH projects’ process openness by analysing their usage of collaboration tools, for example social media, wiki, GitHub etc. This empirical study showed that the usage of collaboration tools in OSH projects decreases as the score of open-o-meter decreases, which implies that the open-o-meter measures correctly an OSH project’s process openness. This research not only validates open-o-meter, but also offers an explicit way to measure an OSH project’s process openness that might be very useful for companies to evaluate potential collaborations.