Explanation
Conveys that 'only (Noun) is the case' or 'nothing but (Noun)'.
Formation
Verb-casual + のは + Noun + ぐらいのものだ, い-Adjective + のは + Noun + ぐらいのものだ, etc.
Detailed explanation
The ～のは Noun ぐらいのものだ pattern indicates that something is exclusively or solely that particular Noun, conveying the sense of 'That's the only thing...' or 'There's nothing but...' about a situation.
Examples
Kono shousetsu o yomu no wa hima tsubushi gurai no mono da.
Reading this novel is nothing but a way to kill time.
Kyou no yuushoku de yokatta no wa piza gurai no mono da.
About the only good thing at tonight's dinner was the pizza.
Kono eiga o miru no wa jikan no muda gurai no mono da.
Watching this movie is nothing but a waste of time.
Kare to hanasu no wa sutoresu gurai no mono da.
Talking to him is nothing but stressful.
Practice
Grammar content sourced from hanabira.org.