Quality & testing.

Fasteners are used in critical environments for assembly of equipment or for attachment of switch plates or wall devices. These fasteners are available in a variety of head configurations. All head configurations include some type of recessed cavity to accommodate various drivers which secure them in place. These cavities can be difficult to clean and may harbor microbiological contaminants.

A current solution to this issue includes filling the fastener cavity with silicone. This is not ideal since the silicone can be mechanically disrupted during cleaning, potentially creating an environment that harbors contamination.

A fastener with a flush head would facilitate cleaning and could potentially decrease or eliminate microbiological contamination. The F-head fastener (Flush Fasteners®), manufactured from type 316 L stainless steel, is designed with an automated plunger that seamlessly reverts to a flush position after the tool is removed, with a clearance of less than 6 microns.

This study sought to compare F-head fasteners (flush) and conventional slotted fasteners to determine the level of residual Bacillus subtilis after fastener inoculation and disinfection.

Dry lint-free sterile wipes were saturated with Peridox RTU (PREempt Plus, Contec). A separate wipe was used to clean each fastener, moving unidirectionally away from the center of the steel plate. The fastener surfaces were continually wiped as needed to allow 3 minutes of wet contact time.

After 3 minutes, a sterile 70% isopropyl alcohol (IPA) wipe was used to wipe each fastener and the surfaces were allowed to dry. The fasteners were aseptically removed from the steel plate to 1 ml of HiCap™ neutralizing broth (World Bioproducts) and eluted for 1 minute. The broth was vortexed and then plated in duplicate to tryptic soy agar (TSA). The agar plates were incubated at 35±2°C for 18–20 hours and colony counts were determined.

Thirty-two samples of each fastener type were analyzed, each sample being plated in duplicate to yield 64 colony count values for each fastener (Table 1, Fig. 2).

A paired t-test was chosen to statistically assess the difference in residual Bacillus subtilis remaining on the two fastener types post-disinfection. Since the fastener pair duplicates were processed on the same steel plate, the sample pair duplicates cannot be considered truly independent from one another. Therefore, two different paired t-tests were conducted, each including one sample pair from the 32 sample groups.

Sample group 1 encompassed all odd-numbered pairs and sample group 2 all even-numbered pairs (Table 2).

Four F-head fasteners (lab-identified as samples 1–4) were submitted for salt-spray corrosion testing per ASTM B117, the standard practice for operating salt-spray (fog) apparatus.

Testing was performed using a Singleton 031M-066 environmental chamber (S/N 42-274-011, calibration due 03/01/2025). Distilled water was used in preparing the 5% salt solution. Temperature was recorded twice daily; salt-solution collection rate, specific gravity, and pH were measured continuously through the 168-hour exposure.

Results at 168 hours

Each sample photographed before and after 168 hours of continuous salt-fog exposure: