Thorlabs Inc.
Visit the Screw Thread Adapters page for pricing and availability information

Screw Thread Adapters

  • Imperial, Metric, and Imperial-Metric Adapters
  • M3, M4, M6, 4-40, 6-32, 8-32, and 1/4"-20 Thread Adapters
  • Useful for Mounts, Posts, and Post Holders
  • Two Types of Counterbore Adapters

AI25E8E

Internal 8-32

Internal 1/4"-20

AS4M8E

Internal M4 x 0.7

External 8-32

CBA25E

1/4"-20 Thread

0.40" Outer Diameter

AE8E25E

Internal 8-32

External 1/4"-20

AP6M8E

External M6 x 1.0

External 8-32

MSA8

Internal 4-40

External 8-32

MSA25

Internal 4-40

External 1/4"-20

HW-KIT6

Thread Adapter Kit

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External to External
Internal Threading with External Threaded Stud
Internal to External
Internal to Internal
Threaded Counterbore
Counterbore Adapter Rings
Screw Thread Adapter Kit

Rail Carrier Cross Section with SD1 Counterbore Adapter Ring

Threading Adapters

  • Machined from 303 Stainless Steel
  • Adapt One Common Thread Standard to Another
  • Ideal for Mounting Posts

Thorlabs' selection of thread adapters offers numerous options for switching between M3, M4, M6, 4-40, 6-32, 8-32, and 1/4"-20 thread sizes. Choose from internal-to-external, external-to-external, or internal-to-internal thread adapters. We also offer internal-to-external threaded stud adapters. Our external-to-external and internal-to-external thread adapters can be adjusted with a screwdriver on either end. The internal-to-internal thread adapters and internal-to-external threaded stud adapters feature a through hole to provide additional torque when tightening or loosening.

The Mini-Series thread adapters can be used to make the Mini-Series posts compatible with our extensive range of optical mounts.

Counterbore Adapters

Threaded counterbore adapters are used to convert a counterbore to a threaded hole. A part such as the KM100 kinematic mirror mount features counterbores to provide imperial and metric compatibility. A cap screw is typically used to fasten these mounts to a post, but in some instances it is necessary to attach the mount to a post with a fixed threaded stud. The counterbore adapter allows parts, such as the KM100, to be post mounted when a cap screw cannot be used.

The SD1 is an adapter ring that provides a means to attach 8-32 (M4) tapped components to 1/4"-20 (M6) counterbored parts. One possible use for the SD1 is in a dovetail optical rail setup where the RC1 rail carriers feature a 1/4" (M6) counterbore. Optic mounts are commonly attached to RC1 rail carriers and usually require the SD1 adapter as most optic mounts are 8-32 (M6) tapped.

Thread Adapter Kits

Thread Adapter Kits are available in both imperial and metric varieties. Both kits come packaged in an organizing box with convenient scaled drawing labels and contain our most popular thread adapters. See below for a list of the specific adapters contained in each kit.


Hide Thread Adapters - External to External

Thread Adapters - External to External

Item # Thread A
(External)		 Thread B
(External)		 Length C
Imperial Thread Adapters
AP8E4Ea 8-32 4-40 0.38" (9.7 mm)
AP8E25Ea 8-32 1/4"-20 0.57" (14.5 mm)
Imperial/Metric Thread Adapters
AP8E4Ma,b 8-32 M4 x 0.7 0.48" (12.2 mm)
AP25E6Ma,b 1/4"-20 M6 x 1.0 0.57" (14.5 mm)
AP6M8Ea,b M6 x 1.0 8-32 0.57" (14.5 mm)
Metric Thread Adapters
AP4M3Mb M4 x 0.7 M3 x 0.5 0.38" (9.7 mm)
AP6M4Mb M6 x 1.0 M4 x 0.7 0.57" (14.5 mm)
  • This adapter is included in the HW-KIT6 Imperial Screw Thread Adapter Kit.
  • This adapter is included in the HW-KIT6/M Metric Screw Thread Adapter Kit.

Part Number
Description
Price
Availability
AP4M3M
Adapter with External M4 Threads and External M3 Threads
$2.31
Today
AP6M4M
Adapter with External M6 x 1.0 Threads and External M4 x 0.7 Threads
$2.31
Today
AP8E4M
Customer Inspired! Adapter with External 8-32 Threads and External M4 x 0.7 Threads
$2.31
Today
AP25E6M
Adapter with External 1/4"-20 Threads and External M6 x 1.0 Threads
$2.31
Today
AP6M8E
Adapter with External M6 x 1.0 Threads and External 8-32 Threads
$2.31
Today
AP8E4E
Adapter with External 8-32 Threads and External 4-40 Threads
$2.31
Today
AP8E25E
Adapter with External 8-32 Threads and External 1/4"-20 Threads
$2.31
Today

Hide Thread Adapters - Internal Threading with External Threaded Stud

Thread Adapters - Internal Threading with External Threaded Stud

MSA8 Application
Click to Enlarge
The MSA8 Thread Adapter converts an 4-40-threaded stud into an 8-32-threaded stud.
Item # Thread A
(Internal)		 Thread B
(External)		 Length C Outer Diametera
Imperial Thread Adapters
MSA8 4-40 8-32 0.50" (12.7 mm) 0.40" (10.2 mm)
MSA25 4-40 1/4"-20 0.55" (14.0 mm) 0.50" (12.7 mm)
AS6E8E 6-32 8-32 0.56" (14.2 mm) 0.24" (6.0 mm)
AS8E25Eb 8-32 1/4"-20 0.68" (17.3 mm) 0.40" (10.2 mm)
AS25E8Eb 1/4"-20 8-32 0.61" (15.4 mm) 0.40" (10.2 mm)
Imperial/Metric Thread Adapters
AS8E4M 8-32 M4 x 0.7 0.56" (14.2 mm) 0.25" (6.4 mm)
AS8E6M 8-32 M6 x 1.0 0.68" (17.3 mm) 0.40" (10.2 mm)
AS25E4M 1/4"-20 M4 x 0.7 0.61" (15.4 mm) 0.40" (10.2 mm)
AS25E6M 1/4"-20 M6 x 1.0 0.63" (16.0 mm) 0.38" (9.5 mm)
AS4M8E M4 x 0.7 8-32 0.56" (14.2 mm) 0.25" (6.4 mm)
AS4M25E M4 x 0.7 1/4"-20 0.68" (17.3 mm) 0.40" (10.2 mm)
AS6M8E M6 x 1.0 8-32 0.61" (15.4 mm) 0.40" (10.2 mm)
AS6M25E M6 x 1.0 1/4"-20 0.63" (16.0 mm) 0.38" (9.5 mm)
Metric Thread Adapters
MSA4/M M3 x 0.5 M4 x 0.7 0.50" (12.7 mm) 0.40" (10.2 mm)
MSA6/M M3 x 0.5 M6 x 1.0 0.55" (14.0 mm) 0.50" (12.7 mm)
AS4M6Mc M4 x 0.7 M6 x 1.0 0.68" (17.3 mm) 0.40" (10.2 mm)
AS6M4Mc M6 x 1.0 M4 x 0.7 0.61" (15.4 mm) 0.40" (10.2 mm)
  • This is the outer diameter of the internally threaded section.
  • This adapter is included in the HW-KIT6 Imperial Screw Thread Adapter Kit.
  • This adapter is included in the HW-KIT6/M Metric Screw Thread Adapter Kit.
Mini-Series Thread Adapters
Click to Enlarge
Mini-Series Thread Adapters

Part Number
Description
Price
Availability
MSA4/M
Mini-Series Adapter with External M4 Threads and Internal M3 Threads
$5.95
Today
MSA6/M
Mini-Series Adapter with External M6 Threads and Internal M3 Threads
$5.95
Today
AS4M6M
Adapter with Internal M4 x 0.7 Threads and External M6 x 1.0 Threaded Stud
$4.97
Today
AS6M4M
Adapter with Internal M6 x 1.0 Threads and External M4 x 0.7 Threaded Stud
$4.97
Today
AS8E4M
Adapter with Internal 8-32 Threads and External M4 x 0.7 Threaded Stud
$4.97
Today
AS8E6M
Adapter with Internal 8-32 Threads and External M6 x 1.0 Threaded Stud
$4.97
Today
AS25E4M
Adapter with Internal 1/4"-20 Threads and External M4 x 0.7 Threaded Stud
$4.97
Today
AS25E6M
Adapter with Internal 1/4"-20 Threads and External M6 x 1.0 Threaded Stud
$4.97
Today
AS4M8E
Adapter with Internal M4 x 0.7 Threads and External 8-32 Threaded Stud
$4.97
Today
AS4M25E
Adapter with Internal M4 x 0.7 Threads and External 1/4"-20 Threaded Stud
$4.97
Today
AS6M8E
Adapter with Internal M6 x 1.0 Threads and External 8-32 Threaded Stud
$4.97
Today
AS6M25E
Adapter with Internal M6 x 1.0 Threads and External 1/4"-20 Threaded Stud
$4.97
Today
MSA8
Mini-Series Adapter with External 8-32 Threads and Internal 4-40 Threads
$5.95
Today
MSA25
Mini-Series Adapter with External 1/4"-20 Threads and Internal 4-40 Threads
$5.95
Today
AS6E8E
Adapter with Internal 6-32 Threads and External 8-32 Threaded Stud
$4.97
Today
AS8E25E
Adapter with Internal 8-32 Threads and External 1/4"-20 Threaded Stud
$4.97
Today
AS25E8E
Adapter with Internal 1/4"-20 Threads and External 8-32 Threaded Stud
$4.97
Today

Hide Thread Adapters - Internal to External

Thread Adapters - Internal to External

Item # Thread A
(Internal)		 Thread B
(External)		 Length C
Imperial Thread Adapters
AE4E25Ea 4-40 1/4"-20 0.38" (9.5 mm)
AE6E25E 6-32 1/4"-20 0.38" (9.5 mm)
AE8E25ES 8-32 1/4"-20 0.20" (5.1 mm)b
AE8E25Ea 8-32 1/4"-20 0.38" (9.5 mm)
Imperial/Metric Thread Adapters
AE4E6M 4-40 M6 x 1.0 0.39" (10.0 mm)
AE6E6M 6-32 M6 x 1.0 0.39" (10.0 mm)
AE8E6M 8-32 M6 x 1.0 0.39" (10.0 mm)
AE3M25E M3 x 0.5 1/4"-20 0.38" (9.5 mm)
AE4M25E M4 x 0.7 1/4"-20 0.38" (9.5 mm)
Metric Thread Adapters
AE3M6Mc M3 x 0.5 M6 x 1.0 0.39" (10.0 mm)
AE4M6MS M4 x 0.7 M6 x 1.0 0.20" (5.1 mm)b
AE4M6Mc M4 x 0.7 M6 x 1.0 0.39" (10.0 mm)
  • This adapter is included in the HW-KIT6 Imperial Screw Thread Adapter Kit.
  • This adapter features a shorter length for compatibility with more components in the Thorlabs catalog. 
  • This adapter is included in the HW-KIT6/M Metric Screw Thread Adapter Kit.

Part Number
Description
Price
Availability
AE3M6M
Adapter with Internal M3 x 0.5 Threads and External M6 x 1.0 Threads
$4.97
Today
AE4M6MS
Adapter with Internal M4 x 0.7 Threads and External M6 x 1.0 Threads, 5.1 mm Length
$4.97
Today
AE4M6M
Adapter with Internal M4 x 0.7 Threads and External M6 x 1.0 Threads, 10.0 mm Length
$4.97
Today
AE4E6M
Adapter with Internal 4-40 Threads and External M6 x 1.0 Threads
$4.97
Today
AE6E6M
Adapter with Internal 6-32 Threads and External M6 x 1.0 Threads
$4.97
Today
AE8E6M
Adapter with Internal 8-32 Threads and External M6 x 1.0 Threads
$4.97
Today
AE3M25E
Adapter with Internal M3 x 0.5 Threads and External 1/4"-20 Threads
$4.97
Today
AE4M25E
Adapter with Internal M4 x 0.7 Threads and External 1/4"-20 Threads
$4.97
Today
AE4E25E
Adapter with Internal 4-40 Threads and External 1/4"-20 Threads
$4.97
Today
AE6E25E
Adapter with Internal 6-32 Threads and External 1/4"-20 Threads
$4.97
Today
AE8E25ES
Adapter with Internal 8-32 Threads and External 1/4"-20 Threads, 0.20" Length
$4.97
Today
AE8E25E
Adapter with Internal 8-32 Threads and External 1/4"-20 Threads, 0.38" Length
$4.97
Today

Hide Thread Adapters - Internal to Internal

Thread Adapters - Internal to Internal

Item # Thread A
(Internal)		 Thread B
(Internal)		 Length C Outer Diameter
AI25E8E 8-32 1/4"-20 0.50" (12.7 mm) 0.40" (10.2 mm)
AI6M4M M4 x 0.7 M6 x 1.0 0.50" (12.7 mm) 0.40" (10.2 mm)

Part Number
Description
Price
Availability
AI6M4M
Adapter with Internal M6 x 1.0 Threads and Internal M4 x 0.7 Threads
$5.71
Today
AI25E8E
Adapter with Internal 1/4"-20 Threads and Internal 8-32 Threads
$5.71
Today

Hide Threaded Counterbore Adapters

Threaded Counterbore Adapters

Counterbore Adapter
Click to Enlarge
  • Converts a Counterbored Clearance Hole into a Tapped Hole
  • Slotted Edge for Tightening
  • Designed for Slip Fit with Thorlabs' Counterbores

Threaded counterbore adapters are used to convert a counterbore into a threaded hole. A part such as the KM100 Kinematic Mirror Mount features a counterbore that provides imperial and metric compatibility; a cap screw is typically used to fasten the mount to a post. In some instances, it may be necessary to attach the mount to a post with a fixed threaded stud. The counterbore adapter facilitates this mounting option. These adapters feature a slotted edge that enables tightening or removal.

Item # Thread A
(Internal)		 Outer Diameter B Use in C-Bore
CBA8E 8-32 0.28" (7.0 mm) #8
CBA25E 1/4"-20 0.40" (10.2 mm) 1/4"
CBA4M M4 x 0.7 0.28" (7.0 mm) M4
CBA6M M6 x 1.0 0.40" (10.2 mm) M6

Part Number
Description
Price
Availability
CBA4M
M4 x 0.7 Threaded Counterbore Adapter
$8.74
Today
CBA6M
M6 x 1.0 Threaded Counterbore Adapter
$8.74
Today
CBA8E
8-32 Tapped Counterbore Adapter
$8.74
Today
CBA25E
1/4"-20 Tapped Counterbore Adapter
$8.74
Today

Hide Counterbore Adapter Rings

Counterbore Adapter Rings

SD1 Adapter Ring in RC1 Rail Carrier
Rail Carrier Cross Section with SD1 Counterbore Adapter Ring
  • Allows a #8 (M4) cap screw to be used within a 1/4" (M6) counterbore
  • Solid stainless steel design
  • Sold in packages of 10

The SD1 adapter ring allows a #8 (M4) cap screw to be used within the 1/4" (M6) counterbore of many parts including rail carriers, BA2 mounting bases, etc. Most of our optomechanical components, such as our compact mirror mounts, feature tapped 8-32 (M4) holes, which this adapter is designed for. For example, the VC1 small V-clamp can mount directly to a BA1 base when an SD1 adapter is used with a 8-32 cap screw.


Part Number
Description
Price
Availability
SD1
1/4" (M6) to #8 (M4) Counterbore Adapter Ring, 10 Pack
$9.21
Today

Hide Screw Thread Adapter Kit

Screw Thread Adapter Kit

Adapter Refills
HW-KIT6 Imperial Thread Adapter Kit
Item Qty. Item Qty.
SS* External 8-32 and External 1/4"-20 (AP8E25E) 5 SS* External 8-32 and External M4 x 0.7 (AP8E4M) 5
SS* Internal 8-32 and External 1/4"-20 (AS8E25E) 5 SS* External 8-32 and External 4-40 (AP8E4E) 5
SS* External M6 x 1.0 and External 1/4"-20 (AP25E6M) 5 SS* External 8-32 and Internal 1/4"-20 (AS25E8E) 5
SS* External 8-32 and External M6 x 1.0 (AP6M8E) 5 SS* Internal 4-40 and External 1/4"-20 (AE4E25E) 5
SS* Internal 8-32 and External 1/4"-20  (AE8E25E) 10 - -

Click to Enlarge
HW-KIT6/M Metric Thread Adapter Kit
Item Qty. Item Qty.
SS* External M4 x 0.7 and External M6 x 1.0 (AP6M4M) 5 SS* External 8-32 and External M4 x 0.7 (AP8E4M) 5
SS* Internal M4 x 0.7 and External M6 x 1.0 (AS4M6M) 5 SS* External M4 x 0.7 and External M3 x 0.5 (AP4M3M) 5
SS* External M6 x 1.0 and External 1/4"-20 (AP25E6M) 5 SS* External M4 x 0.7 and Internal M6 x 1.0 (AS6M4M) 5
SS* External 8-32 and External M6 x 1.0 (AP6M8E) 5 SS* Internal M3 x 0.5 and External M6 x 1.0 (AE3M6M) 5
SS* Internal M4 x 0.7 and External M6 x 1.0 (AE4M6M) 10 - -

*Stainless Steel


Part Number
Description
Price
Availability
HW-KIT6/M
Metric Screw Thread Adapter Kit
$152.05
Today
HW-KIT6
Imperial Screw Thread Adapter Kit
$152.05
Today