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Blind threaded inserts offer standard metric internal threads with 30 degree inclusive form coarse pitch self-tapping external threads. We would recommend blind self-tapping inserts (Series STB) for use in applications where fluid ingression along the internal thread could be an issue. The coarse thread of this type of insert is designed to give more strength, particularly when used on composite materials or softer materials such as wood, fibreglass or plastics. We can custom manufacture inserts to drawing, and our standard range spans M2 to M20 sizes in marine grade stainless steel 316 (A4) or stainless steel 303 (A2) - request a quote today.

We also produce a more robust, heavy duty version of the popular M6, M8 and M10 sizes, with a length of 30mm, to give more external surface area and a deeper, courser thread than the standard inserts.  It will also provide more grip strength and is suited to heavier duty applications and are again, available in marine grade stainless steel.

The insert has a 45 degree shoulder with an undercut to seat it when fully inserted, this provides an area where a sealant or bonding agent can be applied to prevent any fluids passing along the external surface of the insert into the host material or the area behind the insert. The lead-in is chamfered at 10 degrees, with three notches milled into it, to help remove host material, provide a sharp cutting edge and assist keeping the insert parallel on insertion. 

Praise For Our Blind Self Tapping Inserts:

"These inserts have been a marvellous find for us. They do the job superbly, save a lot of time over the previous method of installation and the shipwrights find them very easy to use. Keep up the good work."


Blind threaded inserts have an internal and external thread and are self-cutting, and are supplied in a choice of steel, stainless steel 303 or marine grade stainless steel 316.

This range of inserts is manufactured to the dimensions below:


STB Series Blind Self-Tapping Inserts Size Range

Part # Inside Thread Length ID OD OD Thread Type & Pitch Cutting Relief
M4173 M2 7mm M2 x 0.4mm 4.0mm 30 degree flank self tapping P=1.00mm 3 x milled notch
M4604 M3 8mm M3 x 0.5mm 5.0mm 30 degree flank self tapping P=1.00mm 3 x milled notch
M3398 M4 9mm M4 x 0.7mm 6.0mm 30 degree flank self tapping P=1.25mm 3 x milled notch
M3399 M5 10mm M5 x 0.8mm 8.0mm 30 degree flank self tapping P=1.5mm 3 x milled notch
M3320 M6 12mm M6 x 1.0mm 9.0mm 30 degree flank self tapping P=1.75mm 3 x milled notch
M3796 M6 30mm M6 Heavy Duty 18.0mm 30 degree flank self tapping P=3.0mm 3 x milled notch
M3400 M8 15mm M8 x 1.25mm 12.0mm 30 degree flank self tapping P=2.0mm 3 x milled notch
M3779 M8 30mm M8 Heavy Duty 20.0mm 30 degree flank self tapping P=3.0mm 3 x milled notch
M3318 M10 20mm M10 x 1.5mm 14.0mm 30 degree flank self tapping P=2.5mm 3 x milled notch
M3797 M10 30mm M10 Heavy Duty 20.0mm 30 degree flank self tapping P=3.0mm 3 x milled notch
M3319 M12 25mm M12 x 1.75mm 16.0mm 30 degree flank self tapping P=2.75mm 3 x milled notch
M3725 M16 35mm M16 x 2.0mm 25.0mm 30 degree flank self tapping P=3.50mm 3 x milled notch
M3741 M20 40mm M20 x 2.5mm 30.0mm 30 degree flank self tapping P=3.50mm 3 x milled notch


Technifast is an established supplier and manufacturer of specialist engineering fasteners and components. Our large portfolio of precision fasteners spans pins, dowels, spacers, inserts and keys, which we reliably and efficiently supply to industries Worldwide, including automotive, aviation and marine, at competitive prices.

Technifast’s manufacturing division is dedicated to producing small and complex turned parts, using CNC machines to obtain high precision and an excellent surface finish. We are proud of our reputation for producing both high-volume runs of parts and low-volume orders such as prototype manufacturing. Subscribe to our newsletter or get a FREE, no obligation quote today.


Most of our special pins and turned parts are manufactured in stainless steel, including marine grade 316, but we also produce in a diverse range of other materials, including steel, mild steel and brass. We've also upgraded our machining capabilities and can now produce up to 32mm diameter fasteners.

Technifast is an ISO:9001 registered company. This underpins our reliability as we continually monitor and manage quality across all our operations. Download our ISO:9001 Certificate.

Please join our community or contact us for a fast, efficient quotation or to discuss your bespoke precision component and fastener requirements.

Technifast has almost thirty years' experience in providing precision fastenings and bespoke turned parts to a multitude of industries at an international level. 

We provide our customers with a wide range of fastener solutions, underpinned with first-class technical knowledge, enabling our customers' products to operate in a consistent and efficient manner throughout their life-cycle. Get a quote from our Fastener Sales Specialists today.

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