1) How long do they last? The Deere Tine Catalog (http://www.seamusweldon.com/brochures/brochure_16.pdf) has three different grades: 2) How easily do they break? The rental place had a box full of broken ones but no replacements. The Deere Aerator 800 manual says: I made that last line bold. 3) What size tine? There are a wide variety of tine sizes, most available open/side ejecting and closed top ejecting (stronger, more consistant hole) in a wide variety of diameters: 1/4", 3/8", 1/2", 5/8, 3/4" and 1". There are three tine holders; a 'mini' for the 1/4" that holds the tines at 1.4" spacing, and the others, 2". There are three different tine holders, a mini for 6 1/4" tines, one for the large 3/4" and 1" tines, and one for the other size. This stuff can get expensive, with 16 tines running as much as $200, the turf guards $200, tine holders another $400, although the holder, or core deflector should be maintenance items. The rental house had installed what appears to be HD1/4" mini tines, although I think I only counted 4 per holder. Could he have installed them in the wrong holder? He said they do break, but then the Deere catalog says"