SM-Threaded Adapters for Square Filters

  • Mount Square Optics on SM-Threaded Components
  • Ideal for Plate Filters


SM1 (1.035"-40) Adapter for 1" Square Optics


SM2 (2.035"-40) Adapter for 2" Square Optics
(Filter Not Included)





Related Items

Please Wait
Item # SM1FH SM2FH
Accepted Optic Size 1" or 25 mm Square 2" or 50 mm Square
Max Optic Thickness 0.18" (4.6 mm)
Clear Aperture Ø0.95" (Ø24.0 mm) Ø1.90" (Ø48.3 mm)
Threading External SM1 (1.035"-40)
0.25" (6.3 mm) Deepa
External SM2 (2.035"-40)
0.25" (6.3 mm) Deepa
Included Locking Ring SM1NT1 SM2NT1
Outer Diameter 2.00" (50.8 mm) 3.00" (76.2 mm)
  • Without the included 0.11" (2.8 mm) thick locking ring installed.


  • Mount Square Optics onto Internally SM-Threaded Components
  • Spring-Loaded Clips Secure Optic

These adapters accept square optics and have external SM threading for mounting to other internally SM-threaded components, such as lens tubes. Each adapter has two spring-loaded clips that can hold an optic up to 0.18" (4.6 mm) thick. The SM1FH adapter has SM1 (1.035"-40) threads and accepts 1" or 25 mm square optics, while the SM2FH adapter has SM2 (2.035"-40) threads and accepts 2" or 50 mm square optics. The spring-loaded clips can be tightened using a 0.05" (1.3 mm) hex key.

Each adapter includes a locking ring that allows the optic to be positioned in a specific orientation when the adapter is attached to an SM-threaded component. The locking rings can be tightened by using the SPW502 spanner wrench (for Item # SM1NT1) or SPW503 spanner wrench (for Item # SM2NT1). The adapters are also designed with outer diameters that allow them to be mounted in our smooth-bore mirror mounts.

We also offer Fast-Change Filter Holders for use in lens tube systems and a wide variety of Post-Mountable Rectangular Plate Optic Mounts.

Posted Comments:
Nazim Bharmal  (posted 2024-03-14 10:55:18.447)
Regarding the message posted by, Yongjin Sung (posted 2022-01-11 17:10:05.32) I would echo that comment. In addition it becomes useful for all sizes of mounts to have external threads that allow them to be placed into a lens barrel.
jdelia  (posted 2024-03-14 03:47:18.0)
Thank you for the feedback. I have passed this suggestion along to our design engineers.
Dmitry Kovba  (posted 2024-02-18 12:30:39.857)
This filter holder must be threaded on both sides! The other side in it is just some kind of a joke.
cdolbashian  (posted 2024-02-21 04:13:27.0)
Thank you for reaching out to us Dmitry! I am sorry this product has fallen short of your expectations. I will submit this feedback to our engineering team.
Yongjin Sung  (posted 2022-01-11 17:10:05.32)
Hi. This is exactly what I have been looking for except for the size. Do you have a plan to produce a SM05 adapter for 1/2" square optics with the outer diameter of 1"? Thank you.
jgreschler  (posted 2022-01-18 04:53:52.0)
Thank you for reaching out to Thorlabs. At this time we don't have any plans to produce an adapter for 1/2" square filters to a 1" external diameter. I have logged your request in our company product development forum for future reference, we will consider your comment in the future as we look to expand our catalogue.
Katsuya Nozawa  (posted 2021-12-07 09:05:52.463)
Dir sir, I use the SM1FH as transmission grating mount in front of c-mount lens. It works very fine, but I need a cap to protect the grating. I feel happy if you will sell caps, or you will sell SM1FH with SM2 threads for SM2 end cap.
YLohia  (posted 2021-12-23 12:27:27.0)
Hello, thank you for your feedback. While we do not sell such caps at the moment, we will consider your comments in the future as we look to expand our catalog.
Back to Top

SM Thread Adapters for Square Filters

Based on your currency / country selection, your order will ship from Newton, New Jersey  
+1 Qty Docs Part Number - Universal Price Available
SM1FH Support Documentation
SM1FHCustomer Inspired! SM1-Threaded Adapter for 1" Square Filters
SM2FH Support Documentation
SM2FHCustomer Inspired! SM2-Threaded Adapter for 2" Square Filters
Lead Time