A shutter frame is used for hinging the shutter panels to and generally surrounds the panels on three or four sides. The type of recess you have around your window will determine which frame is going to work best for you. If your window has a standard recess of 100 to 150mm then you can fit your shutters using any of the L or Z frames.To decide which is the best option, ask yourself how often you are likely to open the panels back. Shutters mounted next the window using the L frame with open at a 90° angle to the window and protrude into the room whereas shutters mounted at the front of the reveal using the Z frame or outside mount frame will fold back 180 degrees flush against the wall. For bay windows choose the inside mount L fame. If you have a deep reveal, the inside mount with L frame may work best, for example a four feet wide window, with four x 1 foot panels,and one foot deep reveals would allow two shutter panels to bi-fold back neatly to left and two to the right, into the one foot of reveal space. For bay windows choose the inside mount L frame.Choosing one of the three Z frame will help to hide any imperfections in your plastering around the recess corners. Also if as is the case with most openings, the width is slightly different at the top than at the bottom, the Z frame will disguise this and in effect square your window for you.