Does anybody know, What is this "thing" (circled one on photos) on top of buffer on USATC S100 Class or SR USA Class 0-6-0T Tank Engine?

what's this "thing" purpose?

does only UK examples used this "feature" ("thing" - circled one on photos) or not?

any advantages or disadvantages using this "feature" ("thing" - circled one on photos)?  


image source:

[SR USA | Real Life Thomas The Tank Engine Wiki | Fandom](https://real-life-ttte.fandom.com/wiki/SR_USA)

['USA' Class 0-6-0T BR 30064 at Horsted Keynes on the Blueb… | Flickr](https://www.flickr.com/photos/paulkearley/52763120282/) or [Instagram](https://www.instagram.com/p/DLrRSQBt6zM/)

[File:USA Class 30070.JPG - Wikipedia](https://en.wikipedia.org/wiki/File:USA_Class_30070.JPG)

[File:20160713Y269 30065-85.JPG - Wikipedia](https://en.wikipedia.org/wiki/File:20160713Y269_30065-85.JPG)

[https://www.youtube.com/watch?v=CSXcDNNmEp4](https://www.youtube.com/watch?v=CSXcDNNmEp4)

[30064 (WD 1959, SR 64 & BR 30064) – Preserved British Steam Locomotives](https://preservedbritishsteamlocomotives.com/30064-wd-1959-sr-64-br-30064/) 

[Wide world railfans | USA S100 tank built for service in WW2 of which 14 were subsequently purchased for use in Southampton Docks in the UK, | Facebook](https://www.facebook.com/groups/161697958001042/posts/1096968064474022/)

[S100 - Preserved Railway - UK Steam Whats On Guide and Pictures & Video from events from Lee Andrew Davies](https://preservedrailway.weebly.com/s100.html)

[30065 (WD 1968, SR 65, BR DS 237 & BR 30065) – Preserved British Steam Locomotives](https://preservedbritishsteamlocomotives.com/30065-wd-1968-sr-65-br-ds-237-br-30065/)

[File:KESR 22 Maunsell (Southern 62).JPG - Wikipedia](https://en.wikipedia.org/wiki/File:KESR_22_Maunsell_(Southern_62).JPG)

[File:SR USA Class 30070 No. 300 "Frank S Ross" on the Kent & East Sussex Railway - April 2019 - 01.jpg - Wikipedia](https://en.wikipedia.org/wiki/File:SR_USA_Class_30070_No._300_%22Frank_S_Ross%22_on_the_Kent_&_East_Sussex_Railway_-_April_2019_-_01.jpg)

[SR USA Class No. 30072 | Locomotive Wiki | Fandom](https://locomotive.fandom.com/wiki/SR_USA_Class_No._30072)

[Steam Trains | USA class 0-6-0T No 30063, photographer unknown. | Facebook](https://www.facebook.com/groups/1428326127431927/posts/4146580968939749/)

[S USA tanks - MikeMorant](https://mikemorant.smugmug.com/Trains-Railways-British-Isles/SR-and-BRS/S-USA-tanks)

[30070 (WD 1960, SR 70, BR DS 238 & BR 30070) – Preserved British Steam Locomotives](https://preservedbritishsteamlocomotives.com/30070-wd-1969-sr-70-br-ds-238-br-30070/)

[File:Class USA 0-6-0T.jpg - Wikipedia](https://en.wikipedia.org/wiki/File:Class_USA_0-6-0T.jpg)

[File:SR USA 0-6-0T 30073 Eastleigh MPD 70D, August 1966 (9969640295).jpg - Wikipedia](https://en.wikipedia.org/wiki/File:SR_USA_0-6-0T_30073_Eastleigh_MPD_70D,_August_1966_(9969640295).jpg)

[Bluebell Railway Locomotives - Southern Railway "USA" class No. 30064](https://www.bluebell-railway.co.uk/bluebell/pics/usa.html)

[Southern Railway ‘USA’ Class - No. 30073 – 0-6-0T in BR Li… | Flickr](https://www.flickr.com/photos/159239762@N02/51026501497/)

[VIEW USA CLASS 0-6-0T SR STEAM LOCOS](https://www.anistr.com/-/galleries/railway-images-galleries/photos-of-british-railways-1948-1968/photos-of-br-southern-region-steam-locomotives/photos-of-usa-class-0-6-0t-steam-locos)

[VIEW USA CLASS 0-6-0T SR STEAM LOCOS](https://www.anistr.com/-/galleries/railway-images-galleries/photos-of-british-railways-1948-1968/photos-of-br-southern-region-steam-locomotives/photos-of-usa-class-0-6-0t-steam-locos)

[Bluebell Railway - Eric Kemp - Derek-Hayward](https://www.derekhayward.co.uk/BluebellRailway-1/Bluebell-Railway-Eric-Kemp)

[30072 (US Army 1973, SR 72 & BR 30072) – Preserved British Steam Locomotives](https://preservedbritishsteamlocomotives.com/30072-us-army-1973-sr-72-br-30072/)

[SR USA 0-6-0T 1963 | Flickr](https://www.flickr.com/photos/31890193@N08/albums/72157636466328555/)

[SREmG](https://sremg.org.uk/steam/usaclass.shtml)

[SR “USA” class Dock Tank No. WD 1959 (BR 30064) - The Bluebell Railway in Sussex](https://www.bluebell-railway.com/heritage-locomotives/sr-usa-class-dock-tank-no-wd-1959-br-30064/)





What is this thing on top of buffer on USATC S100 Class or SR USA Class 0-6-0T Tank Engine?