Value Through Solutions®

OptiFlow™ (Flow Drill)


Next-Generation Flow Drill Fastener




OptiFlowâ„¢ (Flow Drill)

Fastening into up to 10mm thick aluminum without clearance holes

Eliminating clearance hole collisions with high-strength top layers

Resisting joint leaks with or without clearance holes

Reducing installation time

Suppressing debris through improved point geometry

Improving material flow in brittle casting materials


Traditional Flow Drill Screw Limitations:

Joint thicknesses without clearance holes are limited to 6mm

Suspectable to detrimental clearance hole collisions

Joints are not leak-resistant

Long installation time

Generate significant debris in certain materials

Inconsistent material flow in brittle castings



The OptiFlow™ fastener's modularity allows the designer to build their custom solution by selecting different head, thread, and tip design features to optimize required installation and joint performance.


OptiFlow Overview



Deep Undercut


Large Washer


Underhead Sealer


Sealing Head










Rolok HS®


Traditional (Metric)




Low Torque


High Performance


Low Torque High Performance




fdsFDS® (Flow Drill Fasteners) has been one of Semblex’s most successful licensed products over the past decade. Semblex FDS is heavily utilized in pickup trucks and large SUVs. FDS uses frictional heat to soften metal substrates and “flow” a hole through them. The fastener then forms threads into the hole it formed and tightens the joint like a standard screw. The FDS product itself is over 25 years old. As our customers and industry became more familiar with FDS, they started asking for the fastener to do more. They wanted FDS to go through thicker materials, work better in brittle materials, fasten high-strength steels, eliminate leak paths, and cost less. Semblex decided to try to tackle these customer requests on its own by focusing on small, combinable design changes. 

OptiFlow is a customizable flow drill screw that allows our customers to select multiple design features to create an optimized flow drill screw solution for their intended application. Each design feature has a 2-letter abbreviation to simplify specifying the desired fastener. 

OptiFlow Low Torque TipOptiFlow - Low Torque Tip (LT): The low torque tip was designed to go through thicker materials. Recent innovations in automotive body structure led to thicker aluminum pieces both to protect battery packs and because of increased casting sizes (giga castings). FDS® is limited to 6mm aluminum because going thicker risks the head of the fastener breaking off when it tries to form threads. To fix this issue, we reduced torque during thread forming by making the tip of the fastener slightly larger. This creates a bigger hole we thread into, reducing thread contact and friction and lowering thread-forming torque. This allows us to form threads into thicker parts before we risk breaking the fastener. By making the tip larger, we also reduced the need for 3-4 pitches of lead threads, allowing us to produce a fastener with more full-size threads than a standard FDS at the same under-head length, which is excellent for design packaging.

High Performance TipOptiFlow—High-Performance Tip (HP): This screw tip reduces the chipping challenges by modifying the pinch-pointed parts to round them off while the threads are rolled. This solves the chipping problem without adding cost to the part. 

Optimized tip shape significantly reduces debris generation

Reduced ‘bushing’ cracking in cast materials

Improves ‘bushing’ formation in extruded materials

shvOptiFlow - Sealing Head (SH): With the rise of EVs, many customers have been searching for ways to leakproof their fastening technologies to prevent water from entering the battery box. The traditional approach to sealing was to add a sealing material to the undercut of the flow drill fastener. However, doing this required a clearance hole in the top layer of material to prevent the sealing from contacting displaced material during installation. This was a problem for our customers who did not want to use clearance holes or had issues with tolerances, which led to installations missing the clearance holes. To answer this problem, we came up with a new head design.OptiFlow Sealing Head This new design utilized two undercuts. The first was to capture material displacement during the installation process, while the second outer undercut held a sealing material that could be compressed against the top material. We spent much time leak-testing flow drill fasteners in different configurations with different sealers and head designs. The sealing head design was the only design that did not leak during our tests—patent pending.



OptiCalc® Software validates applications, speeding up engineering development time.


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    Data Sheet(s)    

OptiFlowâ„¢ Brochure