How much time is needed before or after shabbos to say it is "שכר שבת בהבלעה" (shabbos earnings included with weekday earnings).
pull tab rings attached to orange juice containers, grapefruit juice containers, etc. (Making a nice usable opening on Shabbos.);
The Halachas of מוקצה Muktzah. Differentiation and the Status of a Pen;