Can I use these HO block controllers on O gauge train

They might have contacts that are not robust enough to handle the high current used in 0 gauge track circuits. Since they were free (?) try one and see if it gets hot, or if the magic smoke comes out, when powering a large locomotive and a few passenger cars.

Does Atlas or some HO hobbyist group have a website where you might find the contact rating for these switches? Probably a call or email to Atlas will get you the answer. Atlas calls them "connectors" rather than "switches."  One assumes they do that to avoid confusion with turnouts,

Looks like they are rated for 3 amperes per the following response from Atlas to a question on Amazon:

Question:  Can the Atlas Connector be used with O-scale accessories?

Answer:     Atlas Model Railroad Company makes 2 types of Electrical component connectors- #205 HO & N Connector is designed for 3 Amps usage or less (ie. lighting a model house, some lionel accesorries )
Atlas makes a #6927 HD Connector that is used for 10 amp usage (ie. Track blocking)
You should check the Amperage requirements of the accessory that you want to control and then choose the component that meets that requirement.
Thanks for the question!
By Atlas Model Railroad Company SELLER on May 18, 2020

Don,  I use the Atlas Connectors for lights and other accessories on my layout and use the Atlas Selectors for block control and both work fine. 

Most switches are current for the making and breaking contacts, not the flow when connected.     For example, on my old DC lay out, I used RAdio Shack rotary switchers rated at .3 amps for block control, but that was making or breaking contact, not when connected.    I ran lots of old O scale that drew well over 2 amps and never had a failure.  

The contacts might burn out if you had power to the circuit when you closed the switch.    Typically you have power turned off, or nothing on a track when you close the block switch.     The suggestion above to try them is a good one.    My opinion is they will work unless you are running trains in a block and open or close the switch to that block.

I bought some 6 amp DPDT toggle switches I want to use for block control. Are they adaquet?

The toggles should be fine.  

@Don Baird posted:

I’m building a mid-sized O gauge layout and have just been given a nice little HO layout and a boatload of HO parts.
can I use these Atlas HO block controllers as I wire the O gauge layout?

The 6 Amp Toggles will work fine for your Sidings!  I have used them for years, with no problem whatsoever!!

FREDSTRAINS

I have had Atlas Selectors and a Connector on my Control Panel for some 10+ years.  With a Lionel ZW Transformer .    Never had an Issue.

Steve