diff --git a/fab-toolkit/patterning/photolithography-stepper-v1.md b/fab-toolkit/patterning/photolithography-stepper-v1.md
index 8e29a60..1b65236 100644
--- a/fab-toolkit/patterning/photolithography-stepper-v1.md
+++ b/fab-toolkit/patterning/photolithography-stepper-v1.md
@@ -273,7 +273,7 @@ The following steps will benefit from having two or more helpers. In the images
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-33. Screw the camera onto the C-mount threads at the top of the optics. 
+33. Screw the camera onto the [C-mount](https://www.sinoseen.com/c-mount-vs-cs-mount-the-main-difference) threads at the top of the optics. 
 
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