Don't know which type the Irish used, but as far as I know there are 3 types of bajonets for the FN Fal.
Click
here to go to the Dutch wiki about the FN Fal.
The link should go straight to the part about the bajonets, maybe Google Translate can help you out for the text, and if something isn't translated correctly, or doesn't seem right, feel free to contact me and I'll try to translate or explain for you (not that I have much technical knowledge of bajonets, but one can only try, right?).