I recently bought protective BNC caps for my oscilloscope input. When I screw them on or off I need to apply a much greater force than when connecting the probes. Is this normal? Could this damage my oscilloscope inputs?

Thanks in advance for your help

  • \$\begingroup\$ Are you absolutely sure the connector is compatible with the 50 ohm BNC (like the scope), so that it is not meant for 75 ohm BNC (like the video equipment)? They used to use different center pin diameter back in the 80s. \$\endgroup\$
    – Justme
    Apr 19, 2021 at 19:05
  • 1
    \$\begingroup\$ So, you are trying to protect your o-scope (that no doubt cost quite a lot of money hence why would you buy those items) with scrap iron from Amazon? Put things into context. \$\endgroup\$
    – Andy aka
    Apr 19, 2021 at 19:39
  • \$\begingroup\$ I'm not sure what you are protecting against, there are many more fragile items on a scope, the screen, knobs, probes. I always made sure to tell junior engineers/techs the cost of scope probes, they usually had know idea how expensive they were. \$\endgroup\$
    – Mattman944
    Apr 19, 2021 at 21:10

1 Answer 1


Those protective caps probably aren't built to the same precision as the 'scope probe connector.

You're also probably seeing the effects of the roughness or serrations on the surface of the cap where it engages the 'scope connector.

For example, see the difference in these two:

enter image description here enter image description here

Both pictures from Amazon.


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