Some irregular verbs make no changes between the base form and the past tense and past participle.
- Irregular Verbs—Past and Past Participle Forms are the same as the Base Form in these Irregular Verbs
Bet
Bid
Bust
Cast
Cost
Cut
Fit
Hit
Let
Outbid
Preset
Put
Quit
Read
Recast
Reset
Rid
Set
Shed
Shit
Shut
Sit
Slit
Split
Spread
Underbid
Upset
Wed
Wet
See:
http://www.usingenglish.com/irregular-verb-list.html