The silkscreen outline will always be a little bigger all round than the max device dimensions because it has to allow for a certain amount of slop in the pins fitting into slightly oversized holes plus a bit of guard space to allow parts to be placed outline-to-outline without mechanical fouling. I don't know what package you are measuring but the standard plastic 8 pin DIP packaged NE555 is about 10mm long: [https://www.ti.com/lit/ds/symlink/ne555.pdf](https://www.ti.com/lit/ds/symlink/ne555.pdf)  Find and check the datasheet for the part you are using.

I don't think there is a problem here. The footprint 'outline', (that you are measuring), is often bigger than the actual component. This means it can still be seen on the pcb after the component is soldered into place. Its only a 'representation' of the outline and probably won't be the exact dimensions....and it doesn't need to be. The pads for the pins, on the other hand, DO need to be exact, otherwise the component will not physically fit in the holes. As long as the pad spacing, (for a DIP-8 = 2.54mm), and position, (DIP-8 = 7.62mm apart), is correct then thats all that really matters, you could draw the outline as circular if you wanted, its part of the silkscreen and doesn't affect the component directly. I checked out four 555 Ic's from the EasyEDA libraries...  ...and every one of them had that dimension at 10.16mm. On actually measuring some 555 DIP-8 packages I found all to be 9.3mm, the TI datasheet specifies that dimension as between 9.00mm and 10.16 so I guess whoever drew the footprints went by the maximums. Regards.

Hi. Than you both. You were right :)  I suspect that I was sleepless when I wrote this :)