Thubmnails size widht and height

hello
I would like thumbnails images were from a single measure both Horizontal and vertical, ie

horizontal and vertical 140x186 186x140 fixed size proportional not be long because a larger than another changes the structure of theme

see this site

only size

thanks

Hi, I used the square thumbnails plugin because the square does not want that, so this is looking to show me the thumbnails of fixed dimensions, if I upload a 1024x768 image that the thumbnail of 152x130 is just not change, and if I upload a thumbnail image that is 768x1024 to 130x152, I do not change at will the height and width measurements for example these two images

first image
[img]http://culiacan.quetevalga.com/galerias/main.php?g2_view=core.DownloadItem&g2_itemId=399877&g2_serialNumber=2[/img]

second image

[img]http://culiacan.quetevalga.com/galerias/main.php?g2_view=core.DownloadItem&g2_itemId=399880&g2_serialNumber=2[/img]

The first thumbnail is 100x150 and the second is 150x100

the first is a measure resized 427x640 and the second and all are well fixed 640x427 , as I can do that in my gallery

thanks