that is A mix it valve and they are junk
thh cartridge is about a 60 dollar item...
yoou would be a fool not to change out that whole
mess while you got the chance.... just do it.
get a Dleta 1700 faucet for about 125 and change it out
and like cass say ,,,
change out those wimpy flex lines
to the valve too, they wont last much longer either..