ISCG tabs are three bolt holes, concentric with the bottom bracket, that can be used to mount upper and lower chain guides or to tension chains. However, very few frames that use the T47 BB standard integrate ISCG tabs.

This adapter mounts between a T47 bottom bracket and the bottom bracket shell. It may also work with a PF30 shell given the equal dimensions, but press-fit shells and adapters generally don't play well.

The adapter acts as a 2.5mm spacer, and the mounting holes begin 2.5mm outboard from the BB shell. This is a little further out than welded/brazed tabs, but there is no standard for the lateral position of ISCG tabs, and with the right spacers it should work with most chainguides/tensioners.

However, the inboard offset may lead to clearance issues on some carbon frames. I've only mocked it up on a steel frame.