diff --git a/src/util/Sidekick_util.ml b/src/util/Sidekick_util.ml
index c04e8147..33f20506 100644
--- a/src/util/Sidekick_util.ml
+++ b/src/util/Sidekick_util.ml
@@ -6,6 +6,7 @@ module Util = Util
 module Vec = Vec
 module VecI32 = VecI32
 module Vec_float = Vec_float
+module Vec_sig = Vec_sig
 module Bitvec = Bitvec
 
 module IArray = IArray
diff --git a/src/util/VecI32.mli b/src/util/VecI32.mli
index d0f733ac..d3ba52e9 100644
--- a/src/util/VecI32.mli
+++ b/src/util/VecI32.mli
@@ -3,37 +3,13 @@
 
     These vectors are more optimized than {!Vec}. *)
 
-type t
-
-val create : ?cap:int -> unit -> t
+include Vec_sig.S with type elt := int
 
 val ensure_size : t -> int -> unit
 
-val size : t -> int
-
-val clear : t -> unit
-
-val is_empty : t -> bool
-
-val push : t -> int -> unit
-
-val pop : t -> int
-
 val push_i32 : t -> int32 -> unit
 
-val get : t -> int -> int
-
 val get_i32 : t -> int -> int32
 
-val set : t -> int -> int -> unit
-
 val set_i32 : t -> int -> int32 -> unit
 
-val shrink : t -> int -> unit
-
-val iter : f:(int -> unit) -> t -> unit
-val iteri : f:(int -> int -> unit) -> t -> unit
-
-val to_iter : t -> int Iter.t
-
-val pp : t CCFormat.printer
diff --git a/src/util/Vec_float.ml b/src/util/Vec_float.ml
index 8a3ecd89..1c1d72e8 100644
--- a/src/util/Vec_float.ml
+++ b/src/util/Vec_float.ml
@@ -10,8 +10,8 @@ type t = {
 
 let mk_arr_ sz : float_arr = A.create Bigarray.float64 Bigarray.c_layout sz
 
-let create () : t =
-  { sz=0; data=mk_arr_ 16 }
+let create ?(cap=16) () : t =
+  { sz=0; data=mk_arr_ cap }
 
 let[@inline] clear self = self.sz <- 0
 let[@inline] shrink self n = if n < self.sz then self.sz <- n
diff --git a/src/util/Vec_float.mli b/src/util/Vec_float.mli
index 826b69a7..c8c33ebe 100644
--- a/src/util/Vec_float.mli
+++ b/src/util/Vec_float.mli
@@ -3,31 +3,6 @@
 
     These vectors are more optimized than {!Vec}. *)
 
-type t
-
-val create : unit -> t
+include Vec_sig.S with type elt := float
 
 val ensure_size : t -> int -> unit
-
-val size : t -> int
-
-val clear : t -> unit
-
-val is_empty : t -> bool
-
-val push : t -> float -> unit
-
-val pop : t -> float
-
-val get : t -> int -> float
-
-val set : t -> int -> float -> unit
-
-val shrink : t -> int -> unit
-
-val iter : f:(float -> unit) -> t -> unit
-val iteri : f:(int -> float -> unit) -> t -> unit
-
-val to_iter : t -> float Iter.t
-
-val pp : t CCFormat.printer
diff --git a/src/util/Vec_sig.ml b/src/util/Vec_sig.ml
new file mode 100644
index 00000000..16fa5518
--- /dev/null
+++ b/src/util/Vec_sig.ml
@@ -0,0 +1,30 @@
+
+module type S = sig
+  type elt
+  type t
+
+  val create : ?cap:int -> unit -> t
+
+  val size : t -> int
+
+  val clear : t -> unit
+
+  val is_empty : t -> bool
+
+  val push : t -> elt -> unit
+
+  val pop : t -> elt
+
+  val get : t -> int -> elt
+
+  val set : t -> int -> elt -> unit
+
+  val shrink : t -> int -> unit
+
+  val iter : f:(int -> unit) -> t -> unit
+  val iteri : f:(int -> elt -> unit) -> t -> unit
+
+  val to_iter : t -> elt Iter.t
+
+  val pp : t CCFormat.printer
+end