The Hale Pet Door Locking Security Cover is a 1/4" thick King Starboard polymer sheet. It is extremely shock and impact resistant and has a 3/8" diameter locking hole.
These locking covers only work for Hale Pet Door brand pet doors and are not interchangeable with other brands.

If you are unsure of what flap size you have because your current one is damaged or warped, you can measure the pet door frame itself. The sizing chart below shows the Outside Frame Dimensions that should help you distinguish which size you need.
| Flap Size | Flap Dimension | Outside Frame Dimensions |
|---|---|---|
| Small | 5 1/2" w x 7 1/2" h | 8 3/8" w x 10 3/8" h |
| Small Medium | 6 1/2" w x 9 1/2" h | 9 9/16" w x 12 9/16" h |
| Medium | 8 1/2" w x 12 1/2" h | 11 9/16" w x 15 3/8" h |
| Tall Medium | 8 1/2" w x 16" h | 11 9/16" w x 19 1/16" h |
| Large | 11" w x 16" h | 14 1/16" w x 19 1/16" h |
| Tall Large | 11" w x 19 1/2" h | 14 1/16" w x 22 9/16" h |
| Tall Large Plus | 11" w x 23 1/2" h | 14 1/16" w x 26 9/16" h |
| Extra Tall Large | 11" w x 27 1/2" h | 14 1/16" w x 30 9/16" h |
| Extra Large | 14" w x 19 1/2" h | 17 1/16" w x 22 9/16" h |
| Extra Large Plus | 14" w x 23 1/2" h | 17 1/16" w x 26 9/16" h |
| Giant | 15 1/2" w x 27 1/2" h | 18 9/16" w x 30 9/16" h |
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