Raspberry Pi Pico to Arduino Uno adapter relies on FlexyPins for castellated holes - CNX Software

Solder Party's "Raspberry Pi Pico to Uno FlexyPin Adapter" uses FlexyPins to secure the Pico board to the adapter using its castellated holes.

Surface-mount connectors hold castellated modules

Arduino News - Page 8 of 100 - CNX Software - Embedded Systems News

Low Stock - Pimoroni

A perfect HAT/adapter for Raspberry Pi to utilize Arduino shield, plus it comes with XBee adapter. This is a HAT for Raspberry Pi to enable Arduino

Adapter Board for Arduino & Raspberry Pi

Adapters Solder Party

Solder Party's FlexyPin Adapter offers a swift way to bring the Uno form-factor to the Raspberry Pi Pico

Adapters Solder Party

Low Stock - Pimoroni

Adapters Solder Party

ClipZin PCB connector review — The MagPi magazine

Raspberry Pi Pico FlexyPin Adapter