## 4 Discussion  
Sampling in the worker's breathing zone is one of the most applicable way to assess worker's personal exposure. To get correct positioning in the breathing zone, both commercial and custom-made harnesses may be used. Clamps, tapes, and zip-ties are currently used to attach sampler systems to the harness, creating issues with secureness of the hold, unprofessional looks, and hygienic problems. Designing specifically for AM and 3D printing, the novel design of a universal clip system will help create an aesthetically professional and securely attachable sampler. In this study, such a clip system was designed and tested, first with the hose holder clip and then, the cyclone sampler clip. Both clip systems performed well, although strengthening of hose holder's \"prongs\" is suggested. The field test showed that especially the cyclone sampler clip is ready for real life sampling situations. For the occupational specialists, a short learning curve is needed before use of clips is instinctual. However, this can be compared with the initial introduction of conventionally used attachment gear and can be circumvented through the supporting documents provided in Appendix A. Field tests also showed that it is important to have back-up clips in case of surprises. Parametric design of the clip can ensure that the fit of the clip can be made to fit any harness as long as width and thickness of the harness is known. Depending on the 3D printer, some adjustments may be needed to find the correct process parameters which is supported by the parametric settings, in particular the clearance. The open source files of the design and availability of 3D printing mean that the clip is obtainable to any person, who needs these kind of clip systems. 3D printing also enables the selection of a range of materials and colors. Using affordable 3D printers means that the costs of the clip systems stay low and the open source nature of the clip system will be able to accommodate customization with minimal additional costs. Therefore, the cost comparison made only on a material level is justified; purchased traditionally manufactured components are compared to the direct material and operating costs of 3D printing. This customization of the clip system could easily be extended to other tooling options as well since the basic design can be altered to hold other kinds of samplers and tools. To which areas the clip system design can be extended, and what are the limitations, is work for the future studies. The cost savings shown in Table 1 are the materials and 3D printer operating costs only and they do account for any labor costs. This is a valid assumption as the time needed to customize the system for specific users is comparable (and perhaps shorter) to the time needed to shop for the correct size of the system online. 3D printers do not need to be monitored during use. Thus, the time to print on any of the systems, although hours, is irrelevant as only the time to set up a print is taken into consideration, which is approximately equivalent to ordering a commercial product online. The time to remove the supports, which is less than 10 min for the devices, can be compared to the time it would take to accept delivery of a package and unpack it. Lastly, once all of the components are gathered, they must be assembled. Assembling the complete system takes a similar amount of time to commercial systems. Finally, it is important to point out the life cycle cost advantages of this system. As all the files are shared, regardless of the source of failure of any of the components, the system is easily repaired from readily available components (e.g., reprint a broken plastic component). This ease of repair and upgrading is simply not available for all the commercial systems, which would demand the purchasing of replacement devices.