GKbokiI don't know this as a 100% fact, but I own a similar replacement headband that I got for the Beyerdynamic DT990 premium: https://drop.com/buy/turbulent-labs-grado-beyerdynamic-headbands . The premium version of the DT990 has larger/longer endcaps similar to the T1 and the headband shown here seems to be made for Beyer headphones with the older style of shorter endcaps. It might be possible to replace the endcaps on the T1, which I ended up doing for my DT990 (luckily my endcaps were cracking anyway) but I also don't know this for sure or how.
In short, I doubt these will fit the T1 without modification of some sort.
Edit: I won't mind being proven wrong. If someone could please link a picture of these headbands on a T1 it would be much appreciated.
PastafarianLemurYeah I was doing all kinds of research and I think this is really for the thinner ones. Not sure why Drop advertises it to be T1 compatible.
GKbokiIt did fit my T5p gen 1. The leather stock band is in good condition, but the foam underneath completely disintegrated -- this might be the reason the Dekoni band fit over the stock headband. If any of the original cushion is still there then this headband might not fit correctly.
GKbokiNo...the foam deteriorated over the years, which reason I needed a replacement headband. The Dekoni headband was able to fit because there was little foam still there.