Tim tells us he and Anthony worked closely together on the project -- saying they "wanted to make something that would have some sentimental value to Karl given that he had a really hard time dealing with his mother's passing."
The honorary bling came out PERFECT ... it features a 48.6 gram yellow/white gold "J' pendant that's infused with 7.78 carats of round/emerald VVS Color E/F diamonds.
There's also a custom, hand-painted red rose with green and blue designs to give it "some pop," according to Tim.
It also comes with a 14k solid two-tone yellow gold/white gold rosary style chain -- and we're told it all cost $16,700.
As we reported, KAT has received a bunch of gifts honoring his mother over the past year ... including custom bags with Jackie's name on them from his GF, Jordyn Woods.