Hole Reducer Bolt for 8 mm T-Slot Aluminium Profiles

OEM / ODM Available Free Sample Available RoHS, REACH, bolt grade test report, material certificate for stainless steel

Hole reducer bolt with stepped M8 to M6 thread for 30 and 40 series aluminium profiles. Adapts M8 tapped centre bore to M6 component fitting. Single-piece, no separate bush.

Wholesale Price Quoted per piece, price breaks at 100 / 500 / 1000 per per piece

Material	Carbon steel
Alloy Grade	Carbon steel grade 10.9, stainless A2 / A4
Temper	custom
Section Size	n/a (piece part)
Slot	Fits 30 series M8 bore and 40 series M8/M10 bore
Length	Total 32 mm: M8 15 mm + step 5 mm + M6 12 mm
Tolerance	Thread 6g, step diameter +/-0.05 mm, length +/-0.5 mm
Surface	Zinc plated / stainless steel A2 or A4
MOQ	No MOQ for stock M8-to-M6; 500 pieces for custom combinations
Lead Time	Stocked M8-to-M6 ships in 2 to 3 days; custom about 2 weeks
Loading Port	Shanghai, Ningbo, Qingdao
Supply Ability	Stocked M8-to-M6 in volume; custom combinations produced to order
Payment Terms	T/T 30 per cent deposit, balance against copy of B/L; L/C at sight for larger orders
Trade Terms	FOB, CIF, CFR, EXW
Certifications	RoHS, REACH, bolt grade test report, material certificate for stainless steel

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01What is a hole reducer bolt?

What does a hole reducer bolt do?

It is a stepped bolt with two different thread diameters on one shank. The larger thread (M8) screws into the profile’s centre bore, which is tapped M8 on 30 and 40 series profiles. The smaller thread (M6) projects from the bore and accepts an M6 fitting — a bracket, a sensor mount, a panel or a levelling foot. It lets you use an M6 component on a profile that has an M8 tapped bore, without re-tapping or adding a separate reducer bush.

Why not just use an M8 bolt and a reducer bush?

You can, but the bush adds two parts (bush plus bolt) and a potential loosening point. The reducer bolt is one piece, with no bush to come loose under vibration. It is also shorter: the stepped section is only 5 mm long, versus a bush that adds 10 to 15 mm of stack height. In tight assemblies where the fitting must sit close to the profile face, the reducer bolt is the only option.

Can I get other thread combinations, like M10 to M6?

Yes, on request. The standard stocked combination is M8 to M6, because that is the most common adaptation: 40 series profiles have M8 tapped centre bores, and many fittings (sensor mounts, cylinder cleats) come with M6 threads. M10 to M8 and M10 to M6 are available as custom items.

02Why you need a reducer: the thread mismatch problem

Aluminium profiles in the 30 and 40 series have a centre bore that is tapped to a specific thread. The 30 series has a 9.5 mm bore tapped M8, and the 40 series has a 12 mm bore tapped M8 or M10. These bores are designed for through-bolting structural joints — tying two profiles together in tension.

The problem arises when you want to mount a component on the bore and the component has a different thread. Many sensor mounts, cylinder cleats and levelling feet have M6 threads, but the bore is M8. You have three options: re-tap the bore to M6 (which weakens the profile wall), use a separate reducer bush (which adds height and a loosening point), or use a hole reducer bolt that bridges the two threads in one piece.

Option	Parts	Stack height	Vibration	Bore damage
Re-tap to M6	1 (M6 bolt)	lowest	standard	enlarges bore — irreversible
Reducer bush + M8 bolt	3 (bush, bolt, nut)	10-15 mm extra	bush can loosen	none
Hole reducer bolt	1 (stepped bolt)	5 mm extra	no bush to loosen	none
Through-bolt M8 + adapter nut	2 (bolt, adapter)	8 mm extra	adapter can loosen	none

03Thread and series compatibility

The hole reducer bolt is designed for profiles with tapped centre bores. The 20 series does not have a tapped bore (the bore is too small at 6 mm for an M8 thread), so reducer bolts are not made for 20 series. The 30 and 40 series both have M8 bores, and the 40 series also has an M10 bore option.

Series	Bore diameter	Bore thread	Reducer A (bore side)	Reducer B (component side)
30 series	9.5 mm	M8 x 1.0	M8	M6
40 series	12.0 mm	M8 x 1.0	M8	M6
40 series	12.0 mm	M10 x 1.5 (optional)	M10	M8
40 series	12.0 mm	M10 x 1.5 (optional)	M10	M6

The M10 bore on 40 series is an optional configuration. Standard 40 series profiles have M8 tapped bores. If you need an M10 bore, specify it when ordering the profile — it cannot be re-tapped in the field because the wall is too thin for the larger thread.

04Series to bolt compatibility chart

The following chart shows which bolt thread can be used in each series, including direct fit (standard thread matching the bore) and reducer fit (using a reducer bolt to adapt to a smaller thread). This is the master reference for selecting fasteners for each profile series.

Series	Bore thread	Direct fit bolt	Reducer bolt (to smaller)
15 series	M4	M4	n/a (bore too small for reducer)
20 series	M5 (untapped 6 mm)	M5 T-slot bolt	n/a (no centre bore)
30 series	M8 x 1.0	M8 through-bolt	M8 to M6 reducer bolt
40 series	M8 x 1.0	M8 through-bolt	M8 to M6 reducer bolt
40 series	M10 x 1.5 (opt.)	M10 through-bolt	M10 to M8 / M10 to M6 reducer
45 series	M10 x 1.5	M10 through-bolt	M10 to M8 / M10 to M6 reducer

The 15 and 20 series do not use reducer bolts because their centre bores are too small or untapped. For those series, T-slot nuts and T-bolts are the only fastening method.

05Stepped bolt design and dimensions

The reducer bolt is a single piece of steel with two thread sections and a stepped shoulder between them. The M8 thread is 15 mm long for full engagement in the aluminium bore. The stepped shoulder is 5 mm long, with a diameter of 9 mm — larger than the M6 thread (6 mm) but smaller than the M8 thread (8 mm), so it forms a natural transition between the two.

The M6 thread is 12 mm long, which is standard for M6 fitting engagement. The total bolt length is 32 mm, which means the M6 thread projects 12 mm from the profile face when the M8 thread is fully engaged in the bore.

Dimension	Value	Note
M8 thread length	15 mm	full engagement in aluminium bore
Step shoulder length	5 mm	diameter 9 mm, transition zone
M6 thread length	12 mm	standard M6 fitting engagement
Total bolt length	32 mm	M8 fully engaged, M6 projects 12 mm
M8 thread pitch	1.0 mm	standard coarse pitch
M6 thread pitch	1.0 mm	standard coarse pitch
Bolt grade	10.9	alloy steel, quenched and tempered
Surface	zinc plated 5-8 micron	or stainless A2

06Torque limits and bore engagement

The torque limit on the M8 side is set by the aluminium bore wall strength. The M8 thread engages 15 mm of aluminium, which has a pull-out strength of about 3.5 kN on a 40 series profile. The maximum torque before the threads start to strip is about 25 Nm. Tightening beyond this will damage the bore and require re-tapping or scrapping the profile.

On the M6 side, the torque limit is set by the component fitting. Most M6 fittings are rated to 10 Nm. Tightening the M6 side beyond 10 Nm may damage the fitting thread or crack the fitting body. The reducer bolt itself is grade 10.9 and can withstand much higher torque, but the aluminium bore and the component fitting are the limiting factors.

Side	Thread	Max torque	Limiting factor
Profile side (M8)	M8 x 1.0	25 Nm	aluminium bore thread (3.5 kN pull-out)
Component side (M6)	M6 x 1.0	10 Nm	component fitting rating
Bolt itself	grade 10.9	45 Nm	not the limiting factor

07When to choose a reducer bolt vs alternatives

Choose a hole reducer bolt

You have an M8 tapped bore but the component has an M6 thread
You want a single-piece solution — no separate bush
Stack height matters — the 5 mm step is shorter than a bush
Vibration environment — no bush to come loose
You want to preserve the bore thread — no re-tapping

Choose an alternative

The component has an M8 thread — use a standard M8 through-bolt
You need to go larger, not smaller (M6 bore to M8 component) — re-tap the bore or use a larger profile
20 series profile — no tapped bore; use T-slot nuts and bolts
The bore is already damaged — re-tap to the next size up and use a standard bolt
You need more than 25 Nm on the bore side — use a through-bolt with nuts on both ends

08Failure modes to design out

What goes wrong	Why it happens	Design it out by
M8 thread strips in aluminium bore	torque exceeds 25 Nm or bore is worn from repeated use	limit torque to 20 Nm; use a thread locker on first installation
M6 thread does not fully engage component	component thread depth is less than 12 mm	check component thread depth before installing; use a shorter M6 section
Bolt loosens under vibration	no anti-loosening feature on the stepped bolt	apply medium thread locker to the M8 bore side before installation
Reducer bolt cannot be removed after tightening	M8 thread locked in bore by corrosion or thread locker	use low-strength thread locker if removal is expected; apply anti-seize
Step shoulder bottoms on profile face	bore is shallower than 15 mm (non-standard profile)	check bore depth before ordering; custom M8 thread length available

09Terms used on this page

Hole reducer bolt: A stepped bolt with two thread diameters — larger on the profile side, smaller on the component side — that adapts a tapped bore to a smaller fitting thread.
Centre bore: The coaxial hole through the centre of a strut profile, tapped for through-bolting structural joints. 30 series: M8, 40 series: M8 or M10.
Stepped shoulder: The transition section between the two thread diameters on a reducer bolt. Its diameter is between the two thread sizes.
Through-bolt: A long bolt that passes through the centre bore and ties two profiles together in tension, independent of the T-slots.
Bore engagement: The length of thread contact between the bolt and the aluminium bore. 15 mm on a standard M8 bore gives about 3.5 kN pull-out.
Pull-out force: The axial force required to strip the threads out of the aluminium bore. Determined by the aluminium alloy and the engagement length.

10Questions buyers ask

What thread combinations are available?

The standard stocked combination is M8 to M6. Custom combinations available on request include M10 to M8 and M10 to M6 for 40 series profiles with the optional M10 bore.

Can I use a reducer bolt in a 20 series profile?

No. The 20 series does not have a tapped centre bore — the bore is 6 mm and untapped. For 20 series, use T-slot nuts and T-bolts in the groove.

How tight can I make the M8 side?

The maximum is 25 Nm. Tightening beyond this will strip the aluminium bore thread. For the first installation, 20 Nm is recommended with a medium thread locker.

Can I remove and re-use the reducer bolt?

Yes, but the aluminium bore thread wears with each cycle. After about 5 insertion cycles, the bore may need re-tapping. Apply anti-seize on the M8 thread if removal is expected.

Do you make stainless steel reducer bolts?

Yes, in A2 and A4 stainless steel. The torque limits are the same because the limiting factor is the aluminium bore, not the bolt.

Can you supply matching M6 fittings?

Yes. We supply a range of sensor mounts, cylinder cleats and levelling feet with M6 threads. Specify the fitting type and quantity when ordering.

What we need to quote hole reducer bolts

The profile series (30 or 40) and the bore thread (M8 or M10).
The component thread (M6 or M8) that the reducer bolt must accept.
The bore depth if non-standard (standard is 15 mm for M8).
The material: carbon steel grade 10.9, or stainless steel A2 or A4.
The quantity per size. Price breaks apply at 100, 500 and 1000 pieces.
Any custom thread combination (e.g. M10 to M8) and the engagement length required.

Send those six items and the quotation comes back with the unit price at each quantity break and the lead time for stocked and custom combinations. Browse the full connecting elements range for related fasteners.

Need reducer bolts for M8 bore to M6 fitting?

Send the series, bore thread, component thread, material and quantity. We quote stocked and custom combinations with lead times.

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