The 210914 adaptor is a 48-pin DIL to 48-pin TSOP Socket / Programming Adaptor for use with a Device Programmer.
It converts a target device in a 48-pin TSOP package (20mm from pin edge to pin edge) into a DIL-48 footprint suitable for plugging into the 48-pin ZIF socket of a Device Programmer.
Please see the 210914 datasheet for a complete explanation of device size and adaptor pin-out. This document can be found by clicking the Download link above.